The aim of the article is to present selected relationships between social trust and the development of a territorial unit. Social trust affects the level of cooperation in society and decides about the competitiveness of a territorial unit [12, p. 7]. The main thesis of the article is the author’s conviction that there is a significant correlation between social trust and the activity of citizens, the consequence of which is the development of territorial units. This relationship applies to different categories of units, the article mainly focuses on municipal units. The conclusions presented are a consequence of the analysis of information sources and surveys carried out in three cities: Cracow, Helsinki and Valletta. The socio-economic situation of Poland, Finland and Malta is varied, also due to historical and political conditions. Social trust in these cities depends on different factors. Everywhere, however, significantly affects the direction of urban development, accelerating and stabilising it. Trust is a component of social capital, which translates into the ability to build an innovative and modern economy. In countries where citizens trust each other, a sense of security increases which significantly affects well-being.