This thesis deals with the problem of effective design and usability evaluation of a natural cosmetics website. Given that the natural cosmetics market constantly grows, natural cosmetics companies are increasingly turning to e-business models to promote their brands and sales. As a result, they start realizing how important it is to effectively and efficiently satisfy their customers’ special needs. Bearing this in mind, the main purpose of the thesis is divided in two parts: 1. to propose a pattern language for the easier and more effective design of natural cosmetics websites putting to use the current design knowledge in the form of design patterns, and 2. to offer a framework for evaluating natural cosmetics websites, based on DEPTH usability evaluation method. To achieve the above mentioned goals, we initially run a bibliographic review on usability evaluation issues, focusing on DEPTH (DEsign PaTterns & Heuristic criteria) usability evaluation method and on the exploitation of pattern language and web design patterns in designing and evaluating interactive systems. Subsequently, we run a short research, on both the natural cosmetics sector and the cosmetics sector in general, in order to investigate the particular market characteristics and the specialized consumer needs. We then look into the needs, characteristics and environment analysis of the potential users of an interactive natural cosmetics system. Based on the analysis of similar systems of natural and conventional cosmetics, we assume the basic features a natural cosmetics website should allocate. These features are then deconstructed and given in an arborescent form. According to the DEPTH method, each feature is related to one or more design patterns; thus, a pattern language is created to effectively design and evaluate a natural cosmetics website. The proposed pattern language includes forty-five design patterns; forty of them are adaptations of existing design patterns, while the other five are new patterns developed for the first time in this thesis in order to cover specific system requirements.