A marching band is a group of instrumental musicians who generally perform outdoors, and who incorporate movement – usually some type of marching and other movements  – with their musical performance. Instrumentation typically includes brass, woodwinds, and percussion instruments and the music usually incorporates a strong rhythmic component suitable for marching. All marching bands use some kind of uniform, often military-style uniforms with shakos, pith helmets, feather plumes, capes, gloves, and the school or organization's name or symbol.

In addition to traditional parade performances, many bands also perform field shows at special events (such as football games) or at competitions. Marching bands are generally categorized by function and by the style of field show they perform. Increasingly, marching bands are performing indoor concerts, in addition to any "pep band" duties, that implement many of the songs, traditions, and flair from outside performances.

Marching bands can be categorized based on primary function, instrumentation, and style.

Active duty military marching bands often perform in parades with other military units and march in the same manner as other military personnel. Due to a lack of competition venues, military personnel, and interest, almost all military marching bands have disappeared from schools in the United States; two notable exceptions are the Fightin' Texas Aggie Band from Texas A&M and the Highty-Tighties of the Virginia Tech Corps of Cadets. There is also a pocket of about 80 high school military marching bands in East Texas. They have formed the National Association of Military Marching Bands in order to preserve the tradition of military marching.

Bugle bands are a subset of military bands that use non valved instruments, typically B flat bugles. Some bugle bands, like Burgess Hill Marching Youth extend their range by using instruments such as the jaghorn. In the UK traditional youth bands compete on the TYMBA (Traditional Youth Marching Bands Association) circuit. TYMBA is an organization that was set up in the 1980s by a like minded group of people to cater specifically for youth bands executing military style drill and music.

Parade bands generally play marches. Instrumentation varies, and can contain anything from bagpipes or fifes and drums all the way to full wind and percussion sections. Many military and veterans' organizations have their own parade bands.

Show bands (field shows) have the main role of performing at sporting events, and competitions, such as American football games. They perform a field show before the game and at halftime (and sometimes after the game as well). Show bands typically march in time to the music, and may also participate in parades and competitions. Show bands contain brass and percussion instruments, but may or may not use woodwinds or a percussion pit. Typically, the show is not merely marching in lines. All show bands march as to create designs, curves, and moving illusions as their music progresses during the show.

Carnival Bands are a UK variant of Show bands. Carnival bands typically march in time to the music, and may also participate in parades and competitions. Carnival Bands contain brass and percussion, but may or may not use woodwinds. The main competition body for carnival bands is The Carnival Band Secretaries League.

Scramble bands are a variation on show bands. They generally do not march in time with the music, but, as their name implies, scramble from design to design and often incorporate comedic elements into their performances. Most of the bands in the Ivy league use this style.

Drum and bugle corps is a genre of marching ensemble descended from military signaling units that is distinctly divided into classic and modern corps. Both groups have long, continuous histories and developments separate from marching bands. As the name implies, bugles and drums form the musical background of the corps, but modern competitive drum corps incorporate other brass instruments and orchestral percussion. Governing bodies of competitive drum and bugle corps include Drum Corps International (for junior corps) and Drum Corps Associates (for all age corps) in America, Drum Corps United Kingdom and Drum Corps Europe in Europe, and Drum Corps Japan in Japan.