The basic ensembles that were developed in the Baroque period existed in the Classical period as well. There were still operas, orchestras, string quartets, and soloists. However, the orchestra was expanded in the classical period. While brass was not a major part of the orchestra in the Baroque period, they were added toward the end and became common instruments in the Classical period.
Both time periods made heavy use of singers, string instruments and woodwind instruments. Brass instruments mainly occurred in solos in the Baroque period and later became part of the orchestra in the Classical period. Some of the most commonly used instruments between both periods are the flute, oboe, bassoon, violin, viola, cello, bass and piano. These instruments formed the basis for a composer's study of instrumentation.
Counterpoint first developed in the 16th century. The study of counterpoint was essential to composers of the Baroque period and the Classical period. By studying counterpoint, composers learned how to combine multiple independent lines. This technique commonly occurred in Baroque music. It also appears in the end of Mozart's "The Marriage of Figaro." While composers of the Classical period were intent on simplifying the music to add clarity to the melodies, it was still an important subject of study.
The concept of binary form was first introduced in the Baroque period. As composers developed music throughout the period, this form developed into sonatas, concertos and symphonies. All of these forms continued to be used in the Classical period. The sonata was especially relevant to Classical structure. During this time period, the sonata was developed to include an exposition, development and recapitulation.