Agile, DevOps, and Waterfall are three different software development methodologies. Waterfall follows a linear, step-by-step approach where each phase is completed before the next begins, making it suitable for projects with fixed requirements but less flexible to change. Agile emphasizes iterative development, frequent feedback, and adaptability, allowing teams to deliver small, incremental updates quickly. DevOps focuses on collaboration between development and operations teams, automating processes to enable continuous integration, testing, and deployment for faster and more reliable software delivery.