The concertmaster (from the German Konzertmeister), first chair (US) or leader (UK) is the principal first violin player in an orchestra (clarinet or oboe in a concert band). After the conductor, the concertmaster is the most significant leader in an orchestra, symphonic band or other musical ensemble.

In an orchestra, the concertmaster is customarily the leader of the first violin section. There is another violin section, the second violins, led by the principal second violin. Any violin solo in an orchestral work is played by the concertmaster (except in the case of a violin concerto, in which case a guest soloist usually plays). It is usually required that the concertmaster be the most skilled musician in the section, experienced at learning music quickly, counting rests accurately and leading the rest of the string section by their playing and bow gestures.

The concertmaster sits to the conductor's left, closest to the audience, in what is called the "first chair," "first [music] stand" or outside of the US "first desk." The concertmaster makes decisions regarding bowing and other technical details of violin playing for the violins, and sometimes all of the string players. The concertmaster leads the orchestra in tuning before concerts and rehearsals, and other technical aspects of orchestra management. Leading the orchestral tuning is not a mere formality; if the concertmaster believes that a section is not adequately tuned, they will signal to the oboe player to play another "A." Several larger orchestras have one or more assistant concertmasters, who lead the orchestra in the concertmaster's absence.

The concertmaster, along with the conductor and section principals, will normally participate in the auditions of important musicians (e.g., principal players) in the orchestra.

In a standard concert band, the concertmaster is the principal clarinet or oboe and leads the ensemble's tuning. The first-chair concertmaster will, in common practice, play all solos for their instrument. Often the lead flautist will receive similar responsibilities to the concertmaster, depending on several factors such as age, skill and time spent in the ensemble. The concertmaster will, in both orchestral and wind band settings, also coordinate with other principals and section leaders, in most cases being their senior in terms of group pecking order.

In brass bands, the role of concertmaster is often filled by the principal solo cornet or trumpet.

The duties and tasks of the concertmaster are many. Primarily, the concertmaster acts as the conduit between conductor and orchestra and is accountable to both parties.

One of the principal tasks of the concertmaster is to provide bowings for the first violins prior to rehearsal. This entails a great knowledge of historical playing styles in addition to complete idiomatic understanding of the mechanics of string playing. Section leaders among the other strings will base their bowings on those of the concertmaster and these section leaders (called principals) may confer during rehearsal in order to ensure unity and cohesion of execution between the string sections. Ensemble cohesion emanates directly from the contact and connection between these vital front desk positions. The concertmaster assumes responsibility for the tone and execution of the entire section of first violins, in addition to performing any solo passages that occur in a given piece.