The main focus of this thesis is interaction forces between colloidal particles in liquids of different polarities. Atomic force microscopy (AFM) colloidal probe was the main technique used for measurements, besides dynamic light scattering (DLS) and electrophoresis in the case of nonpolar solvents. Since the surfaces are often electrostatically stabilized, to obtain a stable dispersion it is important to know how the surfaces are charged, or what the characteristics of the solvent are, in order to predict the amount of charges present in the system. The thesis addresses interactions between charged silica particles in the presence of multivalent coions and experimental evidence of algebraically decaying double layer interactions, both in aqueous solutions. The aggregation behavior of three kinds of particles in nonpolar solvent (decane) in the presence of surfactant dioctyl sodium sulfosuccinate (AOT) is investigated. Finally, interactions in presence of 1:1 electrolytes are measured in solvent with intermediate polarity (isopropanol).