Essential security measures for e-commerce websites include data encryption, secure payment gateways, and robust authentication protocols. SSL (Secure Sockets Layer) certificates are critical, ensuring that data exchanged between users and the site is encrypted and secure. Additionally, implementing multi-factor authentication helps protect user accounts by requiring more than a single password for access. Regular security audits and compliance with standards such as PCI DSS (Payment Card Industry Data Security Standard) are crucial to safeguarding sensitive information. Furthermore, intrusion detection systems and continuous monitoring help identify and mitigate security threats in real-time.