Characteristically, Classical style expresses more than one mood and/or theme, achieving this contrast in many different ways. These methods include flexibility of rhythms, or using different rhythms throughout a piece; subtle changes in dynamics; and the development of four-movement forms with contrasting movements of fast-slow-dance-fast. Introducing a dance movement in a multimovement work is called a minuet. Later, Beethoven coined it a scherzo, literally meaning "musical joke." Different movements in a single composition provided musical interest through contrast. Forms within movements were also varied. A composition might begin in a certain key, move to a different key, then return back home to the first. These different sections are known to us as exposition, development, and recapitulation, and the form of this layout is called sonata form. Composers also used popular folk tunes for melodies, often ones which were of a "singing" lyrical quality. Numerous terms associated with the Classical style are used to describe the emotions of the compositions. Most common are the terms galant, which represents everything modern; empfindsamkeit or empfindsamer Stil, a sensitive style meaning "to feel"; and Sturm und Drang, or "storm and stress," the feelings projected by German art and literature.

Many different musical genres, or types of compositions, were prevalent in the Classical period. Instrumental works became most important, and this period has been recognized as the "golden age of chamber music" (Machlis & Forney 235). Chamber music was intended for the small setting of a salon or chamber and consists of a small group of players who perform as a team (such as the string quartet with two violins, viola, and cello). The piano also began to take its significant place in the chamber music setting with the piano trio (piano, violin, and cello). Haydn was central to the evolution of the string quartet, and it is understood that Haydn and Mozart, Beethoven and Schubert established the true chamber music style, which is in the "nature of friendly conversation among equals" (Machlis & Forney 235).

A musical genre consisting of soloist (such as violin or piano) and orchestra, the concerto evolved as a balance and interaction between the instrument and ensemble. Characteristically, this type of piece has three contrasting movements of fast-slow-fast with the addition of a cadenza, or an elaborated solo passage. Another significant genre of this time was the sonata, written mostly for piano or piano and violin. A sonata is generally defined as a solo instrumental work of three or four varied movements.

Choral music and opera also advanced considerably in the Classical era. Mozart’s Requiem Mass (the "Mass for the Dead"), and Haydn’s Mass in D minor ("Lord Nelson Mass") are most famous. However, secular music grew to be more important than sacred genres. Italian comic operas, called opera buffa, were written for entertainment, depicting common people and typical events. Serious opera then began to fade into the past. Called the lied, the German art song was also important to vocal music. Voice parts dominated the accompaniment in the 18th century, but they became more like equal partners as the genre evolved. German publishers issued more than 750 collections of lieder with piano accompaniment in the second half of the 18th century (Grout 467).

Essential to instrumental music was the symphony. The development of the symphony orchestra was different from chamber musical groups. A Classical period orchestra was based on four different families of instruments: strings, woodwinds, brass, and percussion (particularly timpani). Strings dominated the instruments until the woodwinds gained independence in the late works of Haydn and Mozart. Then, the strings served as the bottom foundation, woodwinds played the highest part, and brass were placed in the middle.

Among the prominence of instrumental music was the development of the piano. Evolving in the second half of the 18th century, the piano looked similar to the harpsichord and gradually replaced it as the primary keyboard instrument. Flexibility in dynamics coincided with the rise in popularity of the piano, which had more advanced technical capabilities than the older harpsichord. Called a fortepiano, which translates as "loud/soft," this instrument offered different levels of color through pedaling and quickly-changing dynamics and tone qualities. This was because of an abrupt decay of sound when striking the keys, in contrast to the resonating modern piano. Haydn and Mozart, Beethoven and Schubert played these types of instruments, writing their keyboard music with the now historical fortepianos in mind.