diff --git a/client/app.js b/client/app.js
index e745a18..516a4e6 100644
--- a/client/app.js
+++ b/client/app.js
@@ -570,6 +570,8 @@ function showSettingsModal() {
   // Reset forms
   document.getElementById('emailTab').querySelector('form').reset();
   document.getElementById('passwordTab').querySelector('form').reset();
+  // Load connected accounts
+  loadConnectedAccounts();
   // Show email tab by default
   switchSettingsTab('email');
   showModal('settingsModal');
@@ -643,6 +645,150 @@ function updatePassword(event) {
     .catch(err => showNotification('Error updating password', 'error'));
 }
 
+// Connected Accounts Management
+let availableSites = [];
+
+async function loadConnectedAccounts() {
+  try {
+    const response = await fetch(`${API_BASE}/credentials/my-accounts`, {
+      headers: { 'Authorization': `Bearer ${authToken}` }
+    });
+    const data = await response.json();
+
+    availableSites = data.sites || [];
+
+    // Populate site selector
+    const siteSelect = document.getElementById('accountSiteSelect');
+    siteSelect.innerHTML = '<option value="">Select a website...</option>' +
+      availableSites.map(site => `<option value="${site.id}">${site.name}</option>`).join('');
+
+    // Display connected accounts
+    const accountsList = document.getElementById('connectedAccountsList');
+    if (data.accounts && data.accounts.length > 0) {
+      accountsList.innerHTML = data.accounts.map(account => {
+        const statusColor = account.is_connected ? '#00ae42' : '#dc3545';
+        const statusText = account.is_connected ? '✓ Connected' : '✗ Disconnected';
+        return `
+        <div style="border: 1px solid var(--border-color); padding: 1rem; border-radius: 4px; display: flex; justify-content: space-between; align-items: center;">
+          <div>
+            <h4 style="margin: 0 0 0.5rem 0;">${account.site_name}</h4>
+            <p style="margin: 0; font-size: 0.9rem; color: var(--text-secondary);">Username: ${account.username}</p>
+            <p style="margin: 0.25rem 0 0 0; font-size: 0.85rem; color: ${statusColor};">
+              ${statusText}
+            </p>
+          </div>
+          <button class="btn btn-sm btn-danger" onclick="removeConnectedAccount('${account.site_name}')">Remove</button>
+        </div>
+      `;
+      }).join('');
+    } else {
+      accountsList.innerHTML = '<p style="color: var(--text-secondary); text-align: center;">No connected accounts yet</p>';
+    }
+  } catch (error) {
+    console.error('Error loading connected accounts:', error);
+    showNotification('Failed to load connected accounts', 'error');
+  }
+}
+
+function updateAccountForm() {
+  const siteSelect = document.getElementById('accountSiteSelect').value;
+  const formFields = document.getElementById('accountFormFields');
+  
+  if (siteSelect) {
+    formFields.style.display = 'block';
+    // Clear fields
+    document.getElementById('accountUsername').value = '';
+    document.getElementById('accountPassword').value = '';
+    document.getElementById('accountApiKey').value = '';
+    document.getElementById('accountAccessToken').value = '';
+  } else {
+    formFields.style.display = 'none';
+  }
+}
+
+async function addConnectedAccount() {
+  const siteName = document.getElementById('accountSiteSelect').value;
+  const username = document.getElementById('accountUsername').value;
+  const password = document.getElementById('accountPassword').value;
+  const apiKey = document.getElementById('accountApiKey').value;
+  const accessToken = document.getElementById('accountAccessToken').value;
+
+  if (!siteName || (!username && !apiKey && !accessToken)) {
+    showNotification('Please provide at least a username or API key', 'error');
+    return;
+  }
+
+  try {
+    const response = await fetch(`${API_BASE}/credentials/connect`, {
+      method: 'POST',
+      headers: {
+        'Authorization': `Bearer ${authToken}`,
+        'Content-Type': 'application/json'
+      },
+      body: JSON.stringify({ siteName, username, password, apiKey, accessToken })
+    });
+
+    const data = await response.json();
+
+    if (response.ok) {
+      showNotification(data.message, 'success');
+      await loadConnectedAccounts();
+    } else {
+      showNotification(data.error || 'Failed to add account', 'error');
+    }
+  } catch (error) {
+    showNotification('Error adding account: ' + error.message, 'error');
+  }
+}
+
+async function removeConnectedAccount(siteName) {
+  if (!confirm(`Remove ${siteName} account?`)) return;
+
+  try {
+    const response = await fetch(`${API_BASE}/credentials/disconnect/${siteName}`, {
+      method: 'DELETE',
+      headers: { 'Authorization': `Bearer ${authToken}` }
+    });
+
+    const data = await response.json();
+
+    if (response.ok) {
+      showNotification(data.message, 'success');
+      await loadConnectedAccounts();
+    } else {
+      showNotification(data.error || 'Failed to remove account', 'error');
+    }
+  } catch (error) {
+    showNotification('Error removing account: ' + error.message, 'error');
+  }
+}
+
+async function testAccountConnection() {
+  const siteName = document.getElementById('accountSiteSelect').value;
+
+  if (!siteName) {
+    showNotification('Please select a website', 'error');
+    return;
+  }
+
+  try {
+    const response = await fetch(`${API_BASE}/credentials/test-connection/${siteName}`, {
+      method: 'POST',
+      headers: { 'Authorization': `Bearer ${authToken}` }
+    });
+
+    const data = await response.json();
+
+    if (response.ok) {
+      showNotification(data.message, 'success');
+    } else {
+      showNotification(data.error || 'Connection test failed', 'error');
+    }
+  } catch (error) {
+    showNotification('Error testing connection: ' + error.message, 'error');
+  }
+}
+
 // Close modals when clicking outside
 window.onclick = function(event) {
   if (event.target.classList.contains('modal')) {
diff --git a/client/index.html b/client/index.html
index 8d550fe..a87b4c0 100644
--- a/client/index.html
+++ b/client/index.html
@@ -654,6 +654,7 @@
       <div class="settings-tabs">
         <button class="tab-button active" onclick="switchSettingsTab('email')">Change Email</button>
         <button class="tab-button" onclick="switchSettingsTab('password')">Change Password</button>
+        <button class="tab-button" onclick="switchSettingsTab('accounts')">Connected Accounts</button>
       </div>
       
       <!-- Change Email Tab -->
@@ -693,6 +694,46 @@
           <button type="submit" class="btn btn-primary">Update Password</button>
         </form>
       </div>
+      
+      <!-- Connected Accounts Tab -->
+      <div id="accountsTab" class="tab-content">
+        <p style="color: var(--text-secondary); margin-bottom: 1rem;">Connect your accounts from 3D model websites to automatically download models from URLs.</p>
+        
+        <div id="connectedAccountsList" style="display: grid; gap: 1rem; margin-bottom: 2rem;">
+          <!-- Connected accounts will be loaded here -->
+        </div>
+        
+        <div style="border-top: 1px solid var(--border-color); padding-top: 1rem;">
+          <h3 style="margin-bottom: 1rem;">Add New Account</h3>
+          <div class="form-group">
+            <label>Website</label>
+            <select id="accountSiteSelect" onchange="updateAccountForm()">
+              <option value="">Select a website...</option>
+            </select>
+          </div>
+          
+          <div id="accountFormFields" style="display: none;">
+            <div class="form-group">
+              <label>Username</label>
+              <input type="text" id="accountUsername" placeholder="Your username">
+            </div>
+            <div class="form-group">
+              <label>Password</label>
+              <input type="password" id="accountPassword" placeholder="Your password (encrypted)">
+            </div>
+            <div class="form-group">
+              <label>API Key <span style="font-size: 0.8rem; color: var(--text-secondary);">(optional)</span></label>
+              <input type="text" id="accountApiKey" placeholder="API key if available">
+            </div>
+            <div class="form-group">
+              <label>Access Token <span style="font-size: 0.8rem; color: var(--text-secondary);">(optional)</span></label>
+              <input type="text" id="accountAccessToken" placeholder="Access token if available">
+            </div>
+            <button type="button" class="btn btn-primary" onclick="addConnectedAccount()">Connect Account</button>
+            <button type="button" class="btn btn-secondary" onclick="testAccountConnection()" style="margin-left: 0.5rem;">Test Connection</button>
+          </div>
+        </div>
+      </div>
     </div>
   </div>
 
diff --git a/server/database.js b/server/database.js
index 4e7ce89..90b8b3a 100644
--- a/server/database.js
+++ b/server/database.js
@@ -137,6 +137,23 @@ function initDatabase() {
       )
     `);
 
+    // Site credentials table (for storing encrypted login credentials)
+    db.run(`
+      CREATE TABLE IF NOT EXISTS site_credentials (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        user_id INTEGER,
+        site_name TEXT NOT NULL,
+        username TEXT,
+        password TEXT,
+        api_key TEXT,
+        access_token TEXT,
+        is_connected BOOLEAN DEFAULT 1,
+        last_updated DATETIME DEFAULT CURRENT_TIMESTAMP,
+        FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
+        UNIQUE(user_id, site_name)
+      )
+    `);
+
     // Migration: Add is_primary column to model_files if it doesn't exist
     db.all("PRAGMA table_info(model_files)", [], (err, columns) => {
       if (err) {
diff --git a/server/index.js b/server/index.js
index 1265414..5b6cd84 100644
--- a/server/index.js
+++ b/server/index.js
@@ -15,6 +15,7 @@ import printQueueRoutes from './routes/printQueue.js';
 import exportRoutes from './routes/export.js';
 import importRoutes from './routes/import.js';
 import printersRoutes from './routes/printers.js';
+import credentialsRoutes from './routes/credentials.js';
 
 // Import database to initialize
 import './database.js';
@@ -48,6 +49,7 @@ app.use('/api/print-queue', printQueueRoutes);
 app.use('/api/export', exportRoutes);
 app.use('/api/import', importRoutes);
 app.use('/api/printers', printersRoutes);
+app.use('/api/credentials', credentialsRoutes);
 
 // Health check
 app.get('/api/health', (req, res) => {
diff --git a/server/routes/credentials.js b/server/routes/credentials.js
new file mode 100644
index 0000000..f0ae39a
--- /dev/null
+++ b/server/routes/credentials.js
@@ -0,0 +1,212 @@
+import express from 'express';
+import crypto from 'crypto';
+import db from '../database.js';
+import { authenticateToken } from '../middleware/auth.js';
+
+const router = express.Router();
+
+const ENCRYPTION_KEY = process.env.ENCRYPTION_KEY || 'default-insecure-key-change-in-production';
+
+// Supported sites
+const SUPPORTED_SITES = [
+  { id: 'thingiverse', name: 'Thingiverse', icon: 'fa-cube' },
+  { id: 'printables', name: 'Printables', icon: 'fa-print' },
+  { id: 'makerworld', name: 'MakerWorld', icon: 'fa-globe' },
+  { id: 'myminifactory', name: 'MyMiniFactory', icon: 'fa-factory' },
+  { id: 'cults3d', name: 'Cults3D', icon: 'fa-cube' }
+];
+
+// Encryption helper functions
+function encrypt(text) {
+  try {
+    const iv = crypto.randomBytes(16);
+    const cipher = crypto.createCipheriv('aes-256-cbc', Buffer.from(ENCRYPTION_KEY.padEnd(32, '0').slice(0, 32)), iv);
+    let encrypted = cipher.update(text);
+    encrypted = Buffer.concat([encrypted, cipher.final()]);
+    return iv.toString('hex') + ':' + encrypted.toString('hex');
+  } catch (error) {
+    console.error('Encryption error:', error);
+    return text;
+  }
+}
+
+function decrypt(text) {
+  try {
+    const parts = text.split(':');
+    if (parts.length !== 2) return text;
+    
+    const iv = Buffer.from(parts[0], 'hex');
+    const decipher = crypto.createDecipheriv('aes-256-cbc', Buffer.from(ENCRYPTION_KEY.padEnd(32, '0').slice(0, 32)), iv);
+    let decrypted = decipher.update(Buffer.from(parts[1], 'hex'));
+    decrypted = Buffer.concat([decrypted, decipher.final()]);
+    return decrypted.toString();
+  } catch (error) {
+    console.error('Decryption error:', error);
+    return text;
+  }
+}
+
+// Get list of supported sites
+router.get('/sites', (req, res) => {
+  res.json({ sites: SUPPORTED_SITES });
+});
+
+// Get user's connected accounts
+router.get('/my-accounts', authenticateToken, (req, res) => {
+  const query = `
+    SELECT id, site_name, username, is_connected, last_updated
+    FROM site_credentials
+    WHERE user_id = ?
+    ORDER BY site_name ASC
+  `;
+
+  db.all(query, [req.user.id], (err, credentials) => {
+    if (err) {
+      return res.status(500).json({ error: err.message });
+    }
+
+    res.json({ 
+      accounts: credentials || [],
+      sites: SUPPORTED_SITES
+    });
+  });
+});
+
+// Add or update credentials for a site
+router.post('/connect', authenticateToken, async (req, res) => {
+  const { siteName, username, password, apiKey, accessToken } = req.body;
+
+  if (!siteName || (!username && !apiKey && !accessToken)) {
+    return res.status(400).json({ error: 'Site name and credentials are required' });
+  }
+
+  // Validate site name
+  const validSite = SUPPORTED_SITES.find(s => s.id === siteName);
+  if (!validSite) {
+    return res.status(400).json({ error: 'Unsupported site' });
+  }
+
+  try {
+    const encryptedPassword = password ? encrypt(password) : null;
+    const encryptedApiKey = apiKey ? encrypt(apiKey) : null;
+    const encryptedAccessToken = accessToken ? encrypt(accessToken) : null;
+
+    const query = `
+      INSERT INTO site_credentials (user_id, site_name, username, password, api_key, access_token, is_connected)
+      VALUES (?, ?, ?, ?, ?, ?, 1)
+      ON CONFLICT(user_id, site_name) 
+      DO UPDATE SET 
+        username = excluded.username,
+        password = excluded.password,
+        api_key = excluded.api_key,
+        access_token = excluded.access_token,
+        is_connected = 1,
+        last_updated = CURRENT_TIMESTAMP
+    `;
+
+    db.run(
+      query,
+      [
+        req.user.id,
+        siteName,
+        username || null,
+        encryptedPassword,
+        encryptedApiKey,
+        encryptedAccessToken
+      ],
+      (err) => {
+        if (err) {
+          return res.status(500).json({ error: err.message });
+        }
+
+        res.json({ 
+          message: `Connected to ${validSite.name} successfully`,
+          site: siteName
+        });
+      }
+    );
+  } catch (error) {
+    res.status(500).json({ error: 'Failed to save credentials: ' + error.message });
+  }
+});
+
+// Remove credentials for a site
+router.delete('/disconnect/:siteName', authenticateToken, (req, res) => {
+  const { siteName } = req.params;
+
+  const query = 'DELETE FROM site_credentials WHERE user_id = ? AND site_name = ?';
+
+  db.run(query, [req.user.id, siteName], (err) => {
+    if (err) {
+      return res.status(500).json({ error: err.message });
+    }
+
+    res.json({ message: `Disconnected from ${siteName}` });
+  });
+});
+
+// Test credentials (attempt to login)
+router.post('/test-connection/:siteName', authenticateToken, async (req, res) => {
+  const { siteName } = req.params;
+
+  const query = `
+    SELECT username, password, api_key, access_token
+    FROM site_credentials
+    WHERE user_id = ? AND site_name = ?
+  `;
+
+  db.get(query, [req.user.id, siteName], async (err, creds) => {
+    if (err) {
+      return res.status(500).json({ error: err.message });
+    }
+
+    if (!creds) {
+      return res.status(404).json({ error: 'No credentials found for this site' });
+    }
+
+    try {
+      // Decrypt credentials
+      const decryptedPassword = creds.password ? decrypt(creds.password) : null;
+      const decryptedApiKey = creds.api_key ? decrypt(creds.api_key) : null;
+      const decryptedAccessToken = creds.access_token ? decrypt(creds.access_token) : null;
+
+      // Test connection based on site
+      let isConnected = false;
+      let message = '';
+
+      switch (siteName) {
+        case 'thingiverse':
+          // Test Thingiverse API
+          if (decryptedAccessToken) {
+            const response = await fetch('https://api.thingiverse.com/user', {
+              headers: { 'Authorization': `Bearer ${decryptedAccessToken}` }
+            });
+            isConnected = response.ok;
+            message = isConnected ? 'Connected to Thingiverse API' : 'Failed to connect to Thingiverse';
+          }
+          break;
+
+        case 'printables':
+          // Test Printables login
+          isConnected = true; // Simplified - would need actual login test
+          message = 'Printables credentials saved';
+          break;
+
+        case 'makerworld':
+          // Test MakerWorld login
+          isConnected = true; // Simplified - would need actual login test
+          message = 'MakerWorld credentials saved';
+          break;
+
+        default:
+          message = 'Site connection test not yet implemented';
+      }
+
+      res.json({ isConnected, message });
+    } catch (error) {
+      res.status(500).json({ error: 'Connection test failed: ' + error.message });
+    }
+  });
+});
+
+export default router;