The interfacing of colloidal nano-, microsystems with cell cultures is now well into its second decade. The usage of particles has a various beneficial characteristics that make them attractive for a wide range of technologies. In this report my goal is to highlight how biological media could change the physicochemical properties of colloids, how colloids are internalized by cells, how to distinguish between internalized and membrane-attached colloids, and how stability of colloids may vary upon cell internalization. At the end, the some applications of microparticles as drug delivery carriers will be shown.