In contrast to service quality in traditional facilities (e.g., stores, restaurants, clinics) that enjoyed an extensive research during the last 20 years and resulted in a solid base for service quality measurement and management, service quality that is delivered via the web, termed here electronic service quality, lacks maturity. The present study develops and validates an instrument for measuring electronic service quality of online shopping sites. Using two independent datasets, a conceptual framework of e-service quality is proposed and empirically tested. This research develops an E-SQUAL scale consisting of six dimensions: information quality, web usability, reliability, responsiveness, assurance and personalization. The developed scale demonstrates strong psychometric properties in terms of reliability and validity. Conclusion, implications and limitations of the study are presented.