The topic of this master's thesis is „Brand book in the function of building the brand of the fintech company Aircash“. The main goal of the work is to determine the level of information of the two groups of respondents about the Brand Book and to fine out whether it contibutes to a positive perception of the brand. In the thesis, the term brand book and the term brand are described in more detail in a concise manner.The mission and vision of the Aircash company, its values, persona and personality, voice and tone, and design elements are discussed and described.The work uses methods of synthesis and analysis, descriptions and surveys, and the results of the work contribute to the understanding that the brand book will contribute to the success of the brand.A brand is more than just a logo and a name. The desire to build the success of the brand lies behind the personality in a cohesive way, and the best tool for this is the brand book. Brand book is an inevitable element that every company should have.In order to build a brand on the market, it is extremely important to have properly and strategically defined guidelines that will help the company manage its own identity.The brand book proposed by this thesis is based on communication with the public, with the aim of defining and strengthening the brand of the first Croatian mobile wallet - Aircash.