The problem of homelessness affects every country in the world. Homeless people are pushed to the very margins o fsociety and are the most vulnerable social group. The United Nations estimates that the number of people with the status of a homeless person exceeds a billion. Furthermore, different definitions of homelessness are the reason why it is impossible to estimate the real number of homeless people. It is important that those definitions also include people who are at risk of being homeless, i.e. they are inso-called relative homelessness which has not been incorporated into Croatian legislation. There is also the definition which describes homelessness as “a result of a complex interaction between unfavourable structural and individual events.” Knowing the cause contributes to a better under standing of the problem, to a better planning and implementing the measures and services which meet the real needs of the users. This is why this paper focuses on the causes of homelessness. Various research conducted worldwide indicates the following causes of homelessness: long-term poverty, long-term unemployment, single parenting, low level of education, addiction, impaired mental and physical health, weak social network, imprisonment and losing a home. They are categorised into 4 groups of factors which increase the possibility of becoming homeless: structural, institutional, interpersona lrelations and individua lcharacteristics. It is important to understand that there is no tonly one risk factor whic hleads to homelessness. A person becomes homeless due to an interaction between structural and individual factors.