This thesis aimed to investigate and understand the properties of foams and foam liquid films stabilised by colloidal solid particles, in the absence of any surface active substances, e.g. surfactants. Foams occur as end products or during the processing of products in many industries, including detergents, food and the cosmetic industries. A controlled level of foam formation is desirable in many consumer products. Therefore understanding the mechanisms for their control was also important in this research. Colloidal particles act in many ways like traditional surfactant molecules but offer distinct advantages. The main advantage is that particle-stabilised foams offer longer stability in comparison to surfactant-stabilised foams. Most of the studies, however, were focused on mixtures of surfactant systems and solid particles. Physical mechanisms for foam formation in the presence of colloidal particles alone are less known. However, in response to an increasing interest for this subject, a number of research papers on foams stabilised by solid particles alone have been published recently and during the past 5 years.