Although complementary, these three disciplines focus on different aspects of service delivery:

• ITIL provides a holistic service management framework, covering processes, practices, value streams, governance, and continual improvement.
• DevOps focuses on collaboration between development and operations, emphasizing automation, rapid deployment, and continuous delivery.
• SRE (Site Reliability Engineering), developed by Google, applies software engineering principles to ensure reliability, availability, and performance in large-scale systems.

In short:

• ITIL = service management
• DevOps = speed and collaboration
• SRE = reliability and engineering

All three are often used together in modern IT organizations.