Refinement is one of the cornerstones of a formal approach to software engineering. Refinement is the process of developing a more detailed design or implementation from an abstract specification through a sequence of mathematically-based steps that maintain correctness with respect to the original specification. Work on the foundations of languages such as Z, B, VDM and CSP have led to their widespread use in certain industrial sectors, e.g., those with security or safety critical concerns. In addition to precise specification, formal methods also allow the possibility of precise and verifiable development, as captured by the concept of refinement. The 18th Refinement Workshop was held as part of FLoC 2018 at Oxford, UK.