Engineering interparticle interactions in colloidal systems Colloids abound in nature as well as in technology including pharmacy, paint and food industry etc. Their rich physical and chemical behavior leads to plethora of fundamentally interesting phenomena and provides many ways of their manipulation. In our experiments we use colloids with tightly controlled properties which are suitable as models in statistical physics of atomic or molecular systems. Particularly useful due to the possibility of precisely controlling the interparticle interaction are the magnetic colloids. In my talk I will present several experiments demonstrating how in a (quasi ) 2D systems a complex effective interparticle interactions can be induced by a proper combination of external fields and confinement geometry. I will show two examples: a core-softened and a DLVO-like pair interactions and their effect on colloidal crystal phases in many particle systems.