Comparison of Scrum and Waterfall model Development is phase-based and sequential in waterfall model.But In scrum development is iterative and incremental.Waterfall model eliminate end uncertainty first, and then means uncertainty.But scrum reduce uncertainties simultaneously.Make each decision in its proper phase in waterfall model. But scrum keep options open.Waterfall model have all of the correct information up front to create the requirements and plans.Whereas in scrum we can’t get right information up front.Change is disrupt the plans and expensive, so it should be avoided in waterfall model.But scrum embraces change in an economically sensible way.Cost of delay is rarely considered in waterfall model. But scrum always consider cost of delay.In waterfall model conformance is considered a primary means of achieving a good result.Whereas in scrum adapt and replan rather than conform to a plan.Waterfall model clearly explains progress by progressing through stages or phases.But scrum measures progress by validating working assets.In waterfall model quality comes at the end, after an extensive test-and-fix phase.Whereas in scrum the quality builds from the beginning.Comparison of Extreme Programming and Iterative model In XP user stories are written, but in iterative model clear, comprehensive requirements have been defined. In designing phase, XP consideration on keeping things as simple as possible and as long as possible, but in iterative model less time is spent on documenting and more on designing. In both methods product is given in the form of pieces, but in extreme programming refactoring is done to avoid cheap productionXP reduces the risks related to programming and project failure. XP ensures that the client gets exactly what they want.In iterative model most risks can be identified during iteration and higher risks can be dealt with as an early priorityXP offering constant feedback, demonstrating the software early and often, listening carefully, and making any changes needed. Sprints help the team move in the right direction. In iterative model customer feedback is based on working products rather than technical specifications. In XP each pair of programmers works together to develop certain functionality. This process increases software quality, but in iterative model parallel development can be planned.In XP three types of tests are performed Extreme testing, Unit testing and Acceptance testing then product delivered to customer, but in iterative model testing and debugging during smaller iteration is easy and with every increment, operational product is delivered.Comparison of ASD and Spiral modelThe activities in the each development cycle must be justified against the overall project mission in ASD. Spiral model use for mission-critical projects and works well for complex projects. In ASD, development activities should not be task oriented but rather focus on developing working software. In Spiral model software is produced early on in the project lifecycle. Both methods follows iterative process. The development of high risk items should begin as early as possible in ASD. In spiral model risk analysis helps to eliminate and avoid risk. ASD focuses on results, but Spiral model focus on documentation control. In both methods requirements change according to customer’s needs.Both methods are not pre-planned. Both methods are highly adaptive, cost-effective and flexible.