Outreach is an activity of providing services to any populations who might not otherwise have access to those services. A key component of outreach is that the groups providing it are not stationary, but mobile; in other words they are meeting those in need of outreach services at the locations where those in need are. In addition to delivering services, outreach has an educational role, raising the awareness of existing services.
Outreach is often meant to fill in the gap in the services provided by mainstream (often, governmental) services, and is often carried out by non-profit, nongovernmental organizations. This is a major element differentiating outreach from public relations. Compared to staff providing traditional services, Dewson et al. (2006) notes that outreach staff may be less qualified, but is more highly motivated.
Rhodes (1996) distinguishes between three types of outreach: domiciliary (undertaken at individual homes), detached (undertaken in public environments and targeting individuals), and peripatetic (undertaken at public or private environments and targeting organizations rather than individuals). Dewson et al. (2006) lists another type in addition to those three: the satellite type, where services are provided at a dedicated site.
Dewson et al. (2006) list the following tools of outreach: leaflets, newsletters, advertising; stalls and displays, and dedicated events, with the common location being local community institutions such as libraries, community centres, markets and so on. Compared to traditional service providers, outreach services are provided closer to individuals residence, are voluntary, and have fewer, if any, enforceable obligations.
Outreach can target various populations, from sex workers and drug users, to museum goers. The Jewish counter-missionary organization Outreach Judaism describes itself as "an international organization that responds directly to the issues raised by missionaries and cults, by exploring Judaism in contradistinction to fundamentalist Christianity." 
- Kate Hardy; Sarah Kingston; Teela Sanders (16 December 2010). New Sociologies of Sex Work. Ashgate Publishing, Ltd. p. 77. ISBN 978-0-7546-7986-8. Retrieved 16 September 2012.
- Legal Services Research Centre (30 March 2009). Reaching Further: Innovation, Access and Quality in Legal Services. The Stationery Office. pp. 73–74. ISBN 978-0-11-706724-0. Retrieved 17 September 2012.
- "Maximising the Role of Outreach in Client Engagement", Dewson S, Davis S, Casebourne J. Research Report DWPRR 326, Department for Work and Pensions, 2006.
- Baldur Eliasson; Pierce Riemer; Alexander Wokaun (1999). Greenhouse Gas Control Technologies: Proceedings of the 4th International Conference on Greenhouse Gas Control Technologies, 30 August-2 September 1998, Interlaken, Switzerland. Elsevier. p. 244. ISBN 978-0-08-043018-8. Retrieved 17 September 2012.
- Tim Rhodes (1996). Outreach Work with Drug Users: Principles and Practice. Council of Europe. pp. 25–26. ISBN 978-92-871-3110-2. Retrieved 17 September 2012.
- Bonnie Sachatello-Sawyer (1 October 2002). Adult Museum Programs: Designing Meaningful Experiences. Rowman Altamira. p. 53. ISBN 978-0-7591-0097-8. Retrieved 17 September 2012.
- About Us, Outreach Judaism website. Accessed January 9, 2011.