This volume contains the papers presented at the fifth Colloquium on Implementation of Constraint and LOgic Programming Systems (CICLOPS 2005), held in Sitges (Barcelona), Spain, in October 2005, as a satellite workshop of ICLP 2005.

CICLOPS is a workshop that aims at discussing and exchanging experiences on the design, implementation, and optimization of logic and constraint (logic) programming systems, or systems intimately related to logic as a means to express computations. The workshop continues a tradition of successful workshops on Implementations of Logic Programming Systems, previously held with in Budapest (1993), Ithaca (1994) and Portland (1995), the Compulog Net workshops on Parallelism and Implementation Technologies held in Madrid (1993 and 1994), Utrecht (1995) and Bonn (1996), the Workshop on Parallelism and Implementation Technology for (Constraint) Logic Programming Languages held in Port Jefferson (1997), Manchester (1998), Las Cruces (1999), and London (2000), and recently the Colloquium on Implementation of Constraint and LOgic Programming Systems in Paphos (2001), Copenhagen (2002), Mumbai (2003), and Saint-Malo (2004), and the CoLogNet Workshops on Implementation Technology for Computational Logic Systems held in Madrid (2002), and Pisa (2003).

This year, we received 7 paper submissions, of which 6 were accepted for presentation and inclusion in this volume. The workshop coordinators wish to thank the program committee for the effort and willingness put in the evaluation of the papers, and also the organization of ICLP 2005 for their valuable help. Thanks should go also to the authors of the submitted papers for their contribution to make CICLOPS alive.

We hope that the workshop will bring together researchers interested on implementation technology for different aspects of logic and constraint-based languages and systems, in order to contribute to make this event a meeting point for a fruitful exchange of ideas and feedback on recent developments.