diff --git a/src/scripts/index.ts b/src/scripts/index.ts
index bbc5355..a567f07 100644
--- a/src/scripts/index.ts
+++ b/src/scripts/index.ts
@@ -805,8 +805,8 @@ export class TimelineManager {
     // Initialize datetime modal with callback
     this.dateTimeModal = new DateTimeModal((dateTime: Date) => this.setSelectedDate(dateTime));
 
-    // Initialize with user's timezone and a few others
-    this.initializeDefaultTimezones();
+    // Initialize timezones from URL or defaults
+    this.initializeTimezones();
 
     // Listen for settings changes to refresh timeline
     window.addEventListener('settingsChanged', () => {
@@ -814,14 +814,73 @@ export class TimelineManager {
     });
   }
 
+  private initializeTimezones(): void {
+    // Try to parse timezones from URL first
+    const urlTimezones = this.parseTimezonesFromURL();
+
+    if (urlTimezones.length > 0) {
+      this.selectedTimezones = urlTimezones;
+    } else {
+      // Fallback to default timezones
+      this.initializeDefaultTimezones();
+    }
+
+    this.renderTimeline();
+  }
+
   private initializeDefaultTimezones(): void {
     // Get screen-appropriate number of timezone rows
     const { numRows } = getTimelineDimensions();
 
     // Get properly centered timezones with user timezone in the middle
     this.selectedTimezones = getTimezonesForTimeline(numRows);
+  }
 
-    this.renderTimeline();
+  /**
+   * Parse timezones from URL parameters
+   */
+  private parseTimezonesFromURL(): TimeZone[] {
+    const urlParams = new URLSearchParams(window.location.search);
+    const timezonesParam = urlParams.get('timezones');
+
+    if (!timezonesParam) {
+      return [];
+    }
+
+    // Split by comma and decode URI components
+    const timezoneIds = timezonesParam.split(',').map(id => decodeURIComponent(id.trim()));
+    const validTimezones: TimeZone[] = [];
+
+    // Get all available timezones for lookup
+    const allTimezones = getAllTimezonesOrdered();
+    const timezoneMap = new Map(allTimezones.map(tz => [tz.iana, tz]));
+
+    for (const id of timezoneIds) {
+      const timezone = timezoneMap.get(id);
+      if (timezone) {
+        validTimezones.push(timezone);
+      }
+    }
+
+    return validTimezones;
+  }
+
+  /**
+   * Update URL with current timezone selection
+   */
+  private updateURL(): void {
+    const url = new URL(window.location.href);
+
+    if (this.selectedTimezones.length > 0) {
+      // Create timezone IDs and join with commas (don't double-encode)
+      const timezoneIds = this.selectedTimezones.map(tz => tz.iana).join(',');
+      url.searchParams.set('timezones', timezoneIds);
+    } else {
+      url.searchParams.delete('timezones');
+    }
+
+    // Update URL without page reload
+    window.history.replaceState({}, '', url.toString());
   }
 
   public addTimezone(timezone: TimeZone): void {
@@ -829,12 +888,14 @@ export class TimelineManager {
     const exists = this.selectedTimezones.find(tz => tz.iana === timezone.iana);
     if (!exists) {
       this.selectedTimezones.push(timezone);
+      this.updateURL();
       this.renderTimeline();
     }
   }
 
   public removeTimezone(timezone: TimeZone): void {
     this.selectedTimezones = this.selectedTimezones.filter(tz => tz.iana !== timezone.iana);
+    this.updateURL();
     this.renderTimeline();
   }
 
@@ -860,6 +921,10 @@ export class TimelineManager {
     this.dateTimeModal.open();
   }
 
+  public getSelectedTimezones(): TimeZone[] {
+    return [...this.selectedTimezones];
+  }
+
   private renderTimeline(): void {
     const { numHours } = getTimelineDimensions();
 
diff --git a/test/timezone-url-persistence.test.ts b/test/timezone-url-persistence.test.ts
new file mode 100644
index 0000000..39cef20
--- /dev/null
+++ b/test/timezone-url-persistence.test.ts
@@ -0,0 +1,217 @@
+/**
+ * Timezone URL Persistence Tests
+ * Tests for URL parameter handling of selected timezones
+ */
+
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { TimelineManager } from '../src/scripts/index.js';
+import { loadActualHTML } from './setup.js';
+
+describe('Timezone URL Persistence', () => {
+  let timelineManager: TimelineManager;
+
+  beforeEach(() => {
+    // Load the actual HTML from the site
+    loadActualHTML();
+    
+    // Reset URL state
+    window.location.search = '';
+    
+    // Mock history.replaceState
+    vi.spyOn(history, 'replaceState').mockImplementation(() => {});
+  });
+
+  describe('URL Parameter Parsing', () => {
+    it('should initialize with default timezones when no URL parameters', () => {
+      timelineManager = new TimelineManager();
+      const timezones = timelineManager.getSelectedTimezones();
+      
+      // Should have some default timezones
+      expect(timezones.length).toBeGreaterThan(0);
+      
+      // Should include user's timezone
+      const userTz = Intl.DateTimeFormat().resolvedOptions().timeZone;
+      const hasUserTz = timezones.some(tz => tz.iana === userTz);
+      expect(hasUserTz).toBe(true);
+    });
+
+    it('should parse single timezone from URL parameters', () => {
+      window.location.search = '?timezones=America/New_York';
+      timelineManager = new TimelineManager();
+      const timezones = timelineManager.getSelectedTimezones();
+      
+      expect(timezones.length).toBe(1);
+      expect(timezones[0].iana).toBe('America/New_York');
+    });
+
+    it('should parse multiple timezones from URL parameters', () => {
+      window.location.search = '?timezones=America/New_York,Europe/London,Asia/Tokyo';
+      timelineManager = new TimelineManager();
+      const timezones = timelineManager.getSelectedTimezones();
+      
+      expect(timezones.length).toBe(3);
+      expect(timezones.map(tz => tz.iana)).toEqual([
+        'America/New_York',
+        'Europe/London', 
+        'Asia/Tokyo'
+      ]);
+    });
+
+    it('should handle URL-encoded timezone parameters', () => {
+      window.location.search = '?timezones=America%2FNew_York%2CEurope%2FLondon';
+      timelineManager = new TimelineManager();
+      const timezones = timelineManager.getSelectedTimezones();
+      
+      expect(timezones.length).toBe(2);
+      expect(timezones.map(tz => tz.iana)).toEqual([
+        'America/New_York',
+        'Europe/London'
+      ]);
+    });
+
+    it('should ignore invalid timezone identifiers', () => {
+      window.location.search = '?timezones=America/New_York,Invalid/Timezone,Europe/London';
+      timelineManager = new TimelineManager();
+      const timezones = timelineManager.getSelectedTimezones();
+      
+      // Should only include valid timezones
+      expect(timezones.length).toBe(2);
+      expect(timezones.map(tz => tz.iana)).toEqual([
+        'America/New_York',
+        'Europe/London'
+      ]);
+    });
+
+    it('should fallback to default timezones when all URL timezones are invalid', () => {
+      window.location.search = '?timezones=Invalid/Timezone1,Invalid/Timezone2';
+      timelineManager = new TimelineManager();
+      const timezones = timelineManager.getSelectedTimezones();
+      
+      // Should fallback to default behavior (multiple default timezones)
+      expect(timezones.length).toBeGreaterThan(0);
+    });
+  });
+
+  describe('URL Parameter Updates', () => {
+    beforeEach(() => {
+      timelineManager = new TimelineManager();
+    });
+
+    it('should update URL when timezone is added', () => {
+      const newTimezone = {
+        name: 'Tokyo',
+        offset: 9,
+        displayName: 'Japan Standard Time',
+        iana: 'Asia/Tokyo',
+        cityName: 'Tokyo',
+        abbreviation: 'JST'
+      };
+      
+      timelineManager.addTimezone(newTimezone);
+      
+      expect(history.replaceState).toHaveBeenCalled();
+      
+      // Get the URL that was passed to replaceState
+      const calls = vi.mocked(history.replaceState).mock.calls;
+      const lastCall = calls[calls.length - 1];
+      const url = lastCall[2];
+      
+      expect(url).toContain('timezones=');
+      expect(url).toContain('Asia%2FTokyo'); // URL-encoded version
+    });
+
+    it('should update URL when timezone is removed', () => {
+      // First add a timezone to have something to remove
+      const testTimezone = {
+        name: 'Tokyo',
+        offset: 9,
+        displayName: 'Japan Standard Time',
+        iana: 'Asia/Tokyo',
+        cityName: 'Tokyo',
+        abbreviation: 'JST'
+      };
+      
+      timelineManager.addTimezone(testTimezone);
+      vi.clearAllMocks(); // Clear previous calls
+      
+      timelineManager.removeTimezone(testTimezone);
+      
+      expect(history.replaceState).toHaveBeenCalled();
+      
+      // Get the URL that was passed to replaceState
+      const calls = vi.mocked(history.replaceState).mock.calls;
+      const lastCall = calls[calls.length - 1];
+      const url = lastCall[2];
+      
+      // Asia/Tokyo should no longer be in the URL
+      expect(url).not.toContain('Asia/Tokyo');
+    });
+
+    it('should preserve other URL parameters when updating timezones', () => {
+      window.location.search = '?theme=forest-harmony&mode=light';
+      window.location.href = 'http://localhost:3000/?theme=forest-harmony&mode=light';
+      
+      // Create new manager to pick up URL params
+      timelineManager = new TimelineManager();
+      
+      const newTimezone = {
+        name: 'Sydney',
+        offset: 10,
+        displayName: 'Australian Eastern Standard Time',
+        iana: 'Australia/Sydney',
+        cityName: 'Sydney',
+        abbreviation: 'AEST'
+      };
+      
+      timelineManager.addTimezone(newTimezone);
+      
+      // Get the URL that was passed to replaceState
+      const calls = vi.mocked(history.replaceState).mock.calls;
+      const lastCall = calls[calls.length - 1];
+      const url = lastCall[2];
+      
+      expect(url).toContain('theme=forest-harmony');
+      expect(url).toContain('mode=light');
+      expect(url).toContain('timezones=');
+      expect(url).toContain('Australia%2FSydney'); // URL-encoded version
+    });
+
+    it('should remove timezones parameter when no timezones are selected', () => {
+      // Start with a timezone in URL
+      window.location.search = '?timezones=Asia/Tokyo';
+      timelineManager = new TimelineManager();
+      
+      // Remove all timezones
+      const timezones = timelineManager.getSelectedTimezones();
+      timezones.forEach(tz => timelineManager.removeTimezone(tz));
+      
+      // Should have updated URL to remove timezones parameter
+      const calls = vi.mocked(history.replaceState).mock.calls;
+      const lastCall = calls[calls.length - 1];
+      const url = lastCall[2];
+      
+      expect(url).not.toContain('timezones=');
+    });
+  });
+
+  describe('Integration with Settings', () => {
+    it('should work alongside existing settings URL parameters', () => {
+      window.location.search = '?theme=neon-cyber&mode=light&timeFormat=24h&timezones=America/New_York,Europe/London';
+      
+      timelineManager = new TimelineManager();
+      const timezones = timelineManager.getSelectedTimezones();
+      
+      expect(timezones.length).toBe(2);
+      expect(timezones.map(tz => tz.iana)).toEqual([
+        'America/New_York',
+        'Europe/London'
+      ]);
+      
+      // Settings should still work
+      const urlParams = new URLSearchParams(window.location.search);
+      expect(urlParams.get('theme')).toBe('neon-cyber');
+      expect(urlParams.get('mode')).toBe('light');
+      expect(urlParams.get('timeFormat')).toBe('24h');
+    });
+  });
+});
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