Acknowledgments

Since I started my PhD adventure, four years ago, I have received help, advice and support from many people, to all of whom I am really thankful.

First of all, I am really grateful to my supervisors, Ramon López de Màntaras and Carles Sierra, without whom I would have never finished this thesis. Actually, I would have not even started it!

I am also thankful to the Institut d'Investigació en Intel$\cdot$ligència Artificial, my second home (or was it the first?) during these last four years, to all its staff members and specially the rest of PhD students with whom we have had great times.

I also thank Thomas Dietterich for his help and comments, and also for being such an excellent host in my visits to Corvallis.

Jose Sánchez and Madhur Ambastha deserve special thanks for their help on the development of the vision system and the genetic algorithm approach, respectively.

I am also really grateful to my family, who has supported and helped me (and also homed and fed) during these years.

And last, but not least, thanks to all of my friends, to whom I have tried to explain what has kept me so busy during this time. Although they have not helped on the technical issues of the thesis, they have always been there to remind me that a PhD is not incompatible with going out and having fun (some of them reminded it quite often!). To name some of them (in friendship antiquity order): Roger, Fèlix, Cris, Meri(bad), Glòria, Sandra, Albert, Lluc (thanks for pointing out the Czech origin of the word ``robot''), Meri(jem), Dic... Thank you all.

This research has been partially supported by the Spanish MCYT project ARGOS (DPI2000-1352-C02-02), CICYT project number TAP97-1209, CIRIT project CeRTAP and the US-Spain Joint Commission for Scientific and Technological Cooperation. During the four years of my research I have enjoyed a CIRIT doctoral scholarship (2000FI-00191) from Generalitat de Catalunya.