The papers contained in this volume were presented at the fourth edition of the IFIP International Conference on Theoretical Computer Science (IFIP TCS), held August 23-24, 2006 in Santiago, Chile. They were selected from 44 pa­ pers submitted from 17 countries in response to the call for papers. A total of 16 submissions were accepted as full papers, yielding an acceptance rate of about 36%. Papers sohcited for IFIP TCS 2006 were meant to constitute orig­ inal contributions in two general areas: Algorithms, Complexity and Models of Computation; and Logic, Semantics, Specification and Verification. The conference also included six invited presentations: Marcelo Arenas (P- tificia Universidad Catolica de Chile, Chile), Jozef Gruska (Masaryk University, Czech Republic), Claudio Gutierrez (Universidad de Chile, Chile), Marcos Kiwi (Universidad de Chile, Chile), Nicola Santoro (Carleton University, Canada), and Mihalis Yannakakis (Columbia University, USA). The abstracts of those presentations are included in this volume. In addition, Jozef Gruska and Nicola Santoro accepted our invitation to write full papers related to their talks. Those two surveys are included in the present volume as well. TCS is a biannual conference. The first edition was held in Sendai (Japan, 2000), followed by Montreal (Canada, 2002) and Toulouse (France, 2004).