Both are means for capturing requirements and both can be very effective in doing so in comparison to traditional verbose requirement specification documents that runs through several pages.
However there are some differences between them . Both can be used effectively depending on the your team’s structure, domain expertise and experience with that particular product.
There is a great post by Scott Sehlhorst that goes in to a lot of detail.
Differences
- User stories are written from the point of view of a User while a use case is written from the point of view of the system or application that is being designed.
- User stories take the least over head to write and do not go in a lot of detail to explain the context and scenario.
- User stories can be split in to smaller stories to fit them in to sprints.
- Since they are from the point of view of a User they tend address usability issues better.
- User stories help you identify the shortest path to a complete a task and produce a releasable product.
- User stories can be used for planning and prioritizing while use cases are meant explain the problem and solution. Use cases can be used to understand the over all complexity of the project though.
- User stories contain acceptance tests (validation criteria). Use case not: tests cases are documented in detail elsewhere.
- User stories are in theory written on cards (remember the 3 C rule: Card, Conversation, Confirmation): they’re not intended to be archived unlike use cases.
- Use cases provide a more holistic view of the system: precondition, UC diagram, sub use case. Linking user stories is less obvious. This is also a reason why UX and IxD activities are so important in agile contexts !
- Finally, Use cases and user stories were originally associated with two different methodologies (Unified Process vs eXtreme Programming). But both can be used with agile methods and unified process
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