- Unavailability of employment opportunities.
- Poverty, caused by many factors including unemployment and underemployment.
- Lack of affordable healthcare.
- War or armed conflict.
- Mental disorder, where mental health services are unavailable or difficult to access.
- Disability, especially where disability services are nonexistent or poor performing.
- Substance abuse
- Lack of affordable housing. An article in the November 2007 issue of Atlantic Monthly reported on a study of the cost of obtaining the "right to build" (i.e. a building permit, red tape, bureaucracy, etc.) in different U.S. cities. The "right to build" cost does not include the cost of the land or the cost of constructing the house. The study was conducted by Harvard economists Edward Glaeser and Kristina Tobio. According to the chart accompanying the article, the cost of obtaining the "right to build" adds approximately $600,000 to the cost of each new house that is built in San Francisco.
- Domestic violence.
- Relationship breakdown, particularly in relation to young people and their parents.
- Prison release and re-entry into society.
- Natural disaster, including but not limited to earthquakes and hurricanes.
- Forced eviction - In many countries, people lose their homes by government order to make way for newer upscale high rise buildings, roadways, and other governmental needs. The compensation may be minimal, in which case the former occupants cannot find appropriate new housing and become homeless.
- Mortgage foreclosures where mortgage holders see the best solution to a loan default is to take and sell the house to pay off the debt. The popular press made an issue of this in 2008; the real magnitude of the problem is undocumented.
A substantial percentage of the U.S. homeless population are individuals who are chronically unemployed or have difficulty managing their lives effectively due to prolonged and severe drug and/or alcohol abuse. Substance abuse can cause homelessness from behavioral patterns associated with addiction that alienate an addicted individual's family and friends who could otherwise provide support during difficult economic times.
Increased wealth disparity and income inequality causes distortions in the housing market that push rent burdens higher, making housing unaffordable.
Dr. Paul Koegel of RAND Corporation, a seminal researcher in first generation homelessness studies and beyond, divided the causes of homelessness into structural aspects and then individual vulnerabilities.