Application Programming Interfaces (APIs) are an essential mechanism for software reuse on many levels, such as libraries or web services. However, over the past two decades, many researchers have shown inherent problems with APIs, such as providing useful documentation for proper use, detecting correct usage patterns or wrong usages, and migrating between API versions. While these efforts have advanced the state of the art, most of these problems still exist today. We believe it is time to reflect and compare experiences from different perspectives and to come up with new solutions to the above challenges.

The 2nd International Workshop on API Usage and Evolution (WAPI) provides a venue for researchers and practitioners to come together and discuss the open challenges that API users and designers face. For example, how can we measure the quality of an API? How can we accurately rely on client code for identifying patterns when the rule of ``the majority do it right’’ does not always hold (e.g., in security-related APIs)? What is the best way to present API recommendations and API usages to a developer? The goal of the workshop is to identify the current open challenges in the area and define a roadmap for innovative solutions. Together with all workshop participants, we aim to publish this roadmap as a New Ideas Paper, e.g., in ASE’18, ICSE’19, SANER’19, or FSE’19. Before the workshop, the organizers will derive questions from the accepted papers and ask participants for feedback. This will serve as a framework for workshop discussions. After the workshop, the organizers will draft a respective publication from the results of the discussions and ask participants to contribute to it.