For travelers who prefer a more structured and supported experience (i.e. more "handholding"), this is one of the longest-established names in the field. Founded in 1992, it arranges volunteer placements in areas including conservation, teaching, community development, medicine and public health, as well as programs designed specifically for teenagers and families. It generally provides more hands-on organization than a volunteer marketplace, including pre-departure assistance, airport pickup, accommodation and local staff support. Programs can consequently cost considerably more than bare-bones alternatives, but the additional structure can be reassuring for inexperienced travelers. It's particularly worth investigating for volunteers seeking professionally oriented or skills-based projects rather than an informal work exchange.

Read more in my post 5 of the Top Websites for Voluntourism.