Scout leader, Scoutmaster, Scouter, Scout Advisor or Scout Counsellor generally refers to the trained adult leader of a Scout unit. The terms used vary from country to country, over time, and with the type of unit.

There are many different roles a leader can fulfil depending on the type of unit. Positions are usually voluntary and are often divided between "uniform" and "lay" roles. For many, this volunteerism is an avocation.

Uniformed Scout Leaders are primarily responsible for organising the activities of the group, and training the youth members through the Scout programme. Other roles include liaison with parents, districts, or other parties such as the unit's sponsoring (chartered) organisation.

Lay supporters are not always called scout Leaders; although they may assist with activities and training, they do not always hold a formal position and may not have received training. Beyond the Scout programme, lay supporters may take responsibility for administrative tasks such as budgets, managing properties, recruitment, equipment, transport, and many other roles.

The roles of leaders in senior units like Venture Scout, Explorer Scout and Rover Scout sections tend to be consultative, with much of the administration and activity planning in the hand of older Scouts, while in junior units like Cub Scout and Scout sections, the adult leaders need to take a more central role.

Beyond the group are further uniformed positions (sometimes called Commissioners) at levels such as district, county, council or province, depending on the structure of the national organisation. They also work along with lay teams and professionals. Training teams and other related functions are often formed at these levels. Some countries appoint a Chief Scout or Chief Commissioner as the most senior uniformed member.

Scout Leaders participate in a series of training courses, typically aiming for the Wood Badge as the main qualification of an adult leader in Scouting. In most countries, Wood Badge holders can wear a Gilwell scarf, Turk's head knot woggle, and Wood Badge beads.

Scout Leaders are given a formal appointment (called a warrant in many countries). Before appointing an adult leader, most associations perform background checks on candidates to ensure their suitability for working with children.