Merit badges exist to encourage Scouts to explore areas that interest them and to teach them valuable skills in Scoutcraft. The award of merit badges sometimes leads to careers and lifelong hobbies. Scouts earn a merit badge by satisfying specified criteria; a Court of Honor is then held to present the badge. Scouts can earn badges at any point in their Scouting career, although this was not always the case — in the 1960s, Scouts first had to earn the rank of Second Class Scout before being allowed to work on and earn badges.
The higher ranks of Star, Life, and Eagle require merit badges be earned. Certain badges are mandatory to receive these higher ranks. For a few years during the 1980s and 90s, "First Aid" merit badge was a requirement for the First Class Scout rank. Other mandatory badges include "Citizenship in the Community" and "Environmental Science" (see full list).
The number of merit badges required for each of these higher ranks has varied historically, as has the ratio of mandatory merit badges and non-mandatory badges for those ranks. As of 2005, Scouts must earn a total of 21 merit badges for the Eagle Scout rank, 12 of which must be from the mandatory list. Once Scouts attain the Eagle rank, they can earn Eagle Palms, a core requirement of which is earning more merit badges.
A good example of merit badges reflecting changes in the focus of the Scouting program is "Civics", which was originally the only citizenship-related merit badge. In 1952, the BSA placed more emphasis on this area by splitting "Civics" into four separate badges, which were in turn modified several times. Since 1991, the badges in this group are "Citizenship in the Community", "Citizenship in the Nation", "Citizenship in the World", and "Family Life", all of which are currently on the mandatory list for Eagle Scout.