Who is responsible for functional requirements, and who for non-functional ones?

Functional requirements describe what the system should do — specific functions and behaviors. They are usually the responsibility of a business analyst or systems analyst, who gathers and formalizes requirements from clients and users.

Non-functional requirements describe how the system should operate — performance, security, reliability, usability, etc. They are often the responsibility of architects, systems analysts, and quality engineers.

In real projects, responsibilities may overlap:

• The business analyst gathers and clarifies functional requirements.
• Systems analysts and architects formulate non-functional requirements.
• Project managers oversee the fulfillment of all requirements.

For example, a functional requirement: "The user can register via email." A non-functional requirement: "Server response time during registration should not exceed 2 seconds."