As part of this year's SC15 supercomputing conference the APES project is organising a workshop on molecular simulation software. The aim of the workshop is to explore the challenges associated with improving the performance and sustainability of molecular simulation software and thereby enabling the continued delivery of cutting--edge science on constantly evolving hardware platforms. It aims to bring together developers and users of molecular simulation software, experts in high--performance computing, and researchers of relevant numerical methods and algorithms. The workshop will provide a forum for experts to share insights and strategies aimed at continuing to produce software that can push the boundaries in terms of timescales, system sizes and accuracy and to discuss their relative merits and tradeoffs, particularly in light of hardware trends and with an eye on software sustainability. It will function as an opportunity for HPC experts to better understand the challenges faced in developing software for use by a large group of users of HPC resources within both academia and industry, whilst users will gain a better understanding of the state-of-the-art performance characteristics of different packages and how to use these and the machines they run on most efficiently in their research. The workshop will also encourage the exchange of views of users and developers of molecular simulation software with those of other types of high-performance scientific software facing similar challenges. At the same time as considering how to enable high performance we want to provide participants - both developers and users - with the opportunity to reflect on and discuss the impact that software development practices and different ways of meeting the above challenges have on the maintainability, portability, extensibility, interoperability and usability of codes over the longer term.