Requirements engineering is the engineering discipline of establishing user requirements and specifying software systems. It refers to the process of formulating, documenting and maintaining the SW requirements and to the subpart of SW Engineering pertaining to this process. Requirement engineering continues through the lifetime of the system. Requirement engineering is very critical to the success of software project or product. Requirement should be capable of being measured, testable, traceable, action oriented w.r.t. the business need and opportunities. Besides, Requirement should be properly furnished with details which are sufficient for system design. To derive the requirements user need to have clear and thorough understanding of the product(s) to be developed. Preparation of requirements can be done after detail discussion with team members and end user.