The Classical period of European music was preceded by the Baroque period and followed by the Romantic era. The music of the Baroque tended to be fairly complex; it is still best known for its use of counterpoint, in which multiple simultaneous melodies compete for attention. By the standards of the Enlightenment, the music of the late Baroque was too complex, particularly the elaborate counterpoint. A single, clear melody supported by a pleasant harmony was considered more “natural” and egalitarian, requiring no musical training to enjoy it.

Baroque melodies also have a tendency to run on breathlessly for any number of measures. The ideals of neoclassicism, on the other hand, called for balanced, well-proportioned structures, so the ideal Classical melody was built from an even number of phrases, of the same length (often two or four measures). These phrases were often clearly arranged in pairs, with the second phrase of a pair having a strong feeling of answering or completing the idea from the first phrase. (Read about antecedent and consequent phrases for more about this.) This kind of composing not only gives a very balanced structure, it also leads to melodies that are easy for the average person to sing and to remember. Many folk and popular songs have this same phrase structure.

Harmony was also affected by the goals of clarity and simplicity. The basic rules for harmony that have governed Western music for centuries were set in the Baroque period; Classical composers continued to use the same chords, harmonic progressions and cadences as Baroque composers. To create a feeling of simpler, clearer harmony, however, they generally changed chords less often (for a slower harmonic rhythm), and used less chromaticism (notes and chords outside the key). When they did change keys within a piece, it was usually with a very clear modulation using a standard chord progression, in a spot in the music where the form calls for a key change (for example, in the development section of the sonata form).

This emphasis on clarity and simplicity within a balanced structure does seem to have had the effect that these composers of the Enlightenment were seeking - an art music with an unusually universal appeal - and the results have been far-reaching. The composers of the Romantic era, for example, did not reject Classical composition techniques in the way that Classical composers rejected the Baroque; instead, they explored and developed them, gradually adding more and more complexity and difficulty until the general consensus was that all of the possibilities inherent in the tradition had been explored. Popular Western music, meanwhile, using the same "vocabulary" of scales and chords as Classical music, and using them in very similar ways in constructing melodies and chord progressions, has spread in popularity throughout the world, both on its own and in hybrid styles such as jazz and world music. Furthermore, the Western art music tradition itself has also been adopted in numerous places; Western-style orchestras can be found all over the world now, and in some places are more popular than local music traditions. Perhaps the term for this era is used so often to refer to the entire tradition precisely because the Classical style is more accessible to the average listener than most art music.

Form was very important to the Classical composer, and the period also had a lasting effect in this area, particularly on instrumental music forms. It was during the previous period - the Baroque - that composers began to pay close attention to the capabilities of the various instruments. They began to write not only solo music for specific instruments, but also music for mixed ensembles with specified instruments: the beginnings of the modern orchestra. But the most common instrumental music forms of the Baroque - the toccata, fugue, concerto grosso, for example - were largely replaced by forms that matured in the Classical period. The most influential of these are the symphony, the concerto, and the sonata. While each of these forms had important precursors in earlier times, it is the Classical version of the form that has been most influential through the Romantic and modern eras, and is still widely recognized by art-music audiences and performers today.

The symphony may be the form that comes automatically to most people's minds when they think of Western "Classical" music. The form is so popular that many an orchestra calls itself a "symphony orchestra", signaling that it specializes in playing symphonies. The standard symphony has four movements; the inner two usually include a slow movement and a movement based on a dance form or having a dance-like quality. There are several popular choices for the forms of the outer two movements, but some version of sonata form is the most common.

Music for smaller chamber groups such as string quartets and wind quintets, also often follow this four-movement form.

When a solo instrumentalist is featured playing with an orchestra, the most common form on offer is the concerto. A concerto is typically a three-movement piece, with a slow inner movement and two fast outer movements. Again, for each movement, there are many forms that a composer can choose from - dance forms, theme and variations, fugue, rondo - but sonata form is very common, particularly for the first movement.

Like the concerto, a sonata is typically a fast-slow-fast three-movement piece, but the sonata is typically played by a soloist alone, or by a much smaller group of instruments: a soloist with piano accompaniment is very common. As mentioned above, sonata form is found in concertos and symphonies as well as sonatas. In fact, sonata form is used so often in the first movement of multi-movement works that it is sometimes called first-movement form. As with any music-theory term, composers do not feel bound to follow the rules of a form exactly, and there are many standard variations of sonata form. In the most general terms, there are three main parts (leaving aside the possibility of short introduction or ending sections) to a sonata form, which a careful listener can learn to distinguish even without formal musical training. The exposition introduces the main melodic ideas that are the themes for the movement. During the development, these melodic ideas are explored in a variety of different ways, often including taking them through a variety of key changes as well as changes in rhythm and harmony. In the recapitulation the themes return in the original key and in a form close enough to the original to make the listener feel that they have "returned home" after the "wandering" of the development section.

Although the Classical period is generally identified with the second half of the eighteenth century, not every piece written during that period was Classical in style, nor were all Classical-style pieces written during those years. Some composers of that period were not interested in the new style, and continued to compose in the Baroque style.

Drawing a clear line between the Classical and Romantic eras is even more difficult. Ludwig van Beethoven is generally considered to be the most prominent founder of the Romantic style; his early works are considered to be clearly Classical, while his later compositions (the Third Symphony is sometimes used as a dividing line) are considered to be the inspiration for later Romantic composers. Some of those composers were more "Romantic" than others, however. Many popular nineteenth-century composers ignored many of the implications of the Romantic style, and wrote compositions that were essentially Classical.

The earliest composers in the Classical style, such as Johann Stamitz, are very important to music history, but their compositions tend to sound a bit too simplistic to the modern ear, and recordings and performances of their works are uncommon.

Of the strictly-Classical-era composers, Wolfgang Amadeus Mozart is widely held in the highest esteem. His hundreds of compositions include symphonies, concertos, operas, string quartets and other chamber music, instrumental serenades and divertimenti, and masses. This large body of work includes many masterpieces and is a good place to start for anyone wishing to get acquainted with the sound of the Classical style.

Franz Joseph Haydn is the other very famous Classical-era composer. He wrote more than one hundred symphonies, as well as numerous string quartets, concertos for a variety of instruments, and vocal works such as masses and oratorios.

Many of Ludwig van Beethoven's most famous works (the Fifth and Ninth Symphonies, for example), are clearly Romantic in character, but earlier works, including the first two symphonies and the earlier string quartets, piano concertos, and piano sonatas (including the "Moonlight" and "Pathetique") are from his earliest, most Classical-sounding period.

The end of the Classical era was not marked by a rejection of the style, as its beginning had been a rejection of the Baroque. Instead, as composers gained confidence and inspiration, they began to explore, expand, and develop the forms, ensembles, and melodic and harmonic vocabulary of Classical music. Given the impetus towards individualism, innovation and exploration of the nineteenth century, many composers pushed very hard to expand the limits of what was acceptable, and their music has a very different sound than eighteenth-century music, although it is still clearly within the same tradition. Other composers stayed closer to Classical-era ideals, however: Johannes Brahms, Franz Schubert, Felix Mendelssohn, and Gioachino Rossini are among the popular nineteenth-century composers whose music remained largely rooted in the Classical tradition.