Modular aspects of analysing, constructing and verifying executable specifications have received increasing attention in the last years, due to the enormous potential for significant advances in theory and practice. It is well-known that various basic properties and computation / reasoning techniques for executable specifications exhibit a non-modular behaviour in general, thereby impeding the design and verification of complex specifications by systematically combining simpler ones. In this project, the focus is on modular aspects of executable specifications in the framework of equational/rewriting logic, specification and programming. The objectives and envisaged research themes cover the following related fields. Firstly, several foundational issues of combining specifications will be investigated. This includes in particular the study of inheritence criteria for crucial properties of specifications under various practically relevant types of combination mechanisms. Secondly, important pragmatic and operational issues of analysing and constructing complex executable specifications, and of corresponding reasoning and proof techniques are studied. This will be done in connection with contributing improvements to the software systems ELAN (a logical framework based on the rewriting logic) and SPIKE (a theorem prover for first-order logic and inductive reasoning) developed by the PROTHEO team in Nancy. And thirdly, the previous theoretical and conceptual investigations on modular aspects of designing and verifying executable specifications will be applied to practical problems. In particular, it is intended to study specifications of telephone services, in the context of the cooperation between CNET France Telecom and PROTHEO.