Ludwig van Beethoven is one of the most influential figures in the history of classical music. Since his lifetime, when he was "universally accepted as the greatest living composer", Beethoven's music has remained among the most performed, discussed and reviewed in the Western world. Scholarly journals are devoted to analysis of his life and work. He has been the subject of numerous biographies and monographs, and his music was the driving force behind the development of Schenkerian analysis. He is widely considered among the most important composers, and along with Bach and Mozart, his music is the most frequently recorded.

Beethoven expanded the formal and emotional scope – not to mention length – of nearly every genre in which he wrote. While he is most famous for his heightening of the symphonic form, Beethoven also had a crucial influence on the piano sonata, violin sonata, string quartet and piano concerto, among several others. Only in the realm of vocal composition – opera and the mass – was his effect on later generations muted.

Beethoven's stylistic innovations bridge the Classical and Romantic periods. The works of his early period brought the Classical form to its highest expressive level, expanding in formal, structural, and harmonic terms the musical idiom developed by predecessors such as Mozart and Haydn. The works of his middle period were more forward-looking, contributing to the musical language and thinking of the Romantic era, inspiring composers such as Franz Schubert, Felix Mendelssohn, Hector Berlioz, Robert Schumann, Franz Liszt, Richard Wagner, and Johannes Brahms. His late period works were characterized by formal, harmonic, and structural experimentation at the highest level, often pointing toward contrapuntal tendencies and microscopic textures, as well as an increasingly introverted compositional outlook. Though rightly credited as a major harbinger of the Romantic era in music that followed, Beethoven never abandoned fundamental aesthetical paradigms and a generally objective artistic philosophy characterizing musical Classicism to the same extent that later composers such as Berlioz or even Schubert did.

Overview Beethoven's musical output has traditionally been divided into three periods, a classification that dates to the first years after the composer's death in 1827 and was formalised with the publication of Wilhelm von Lenz's influential work Beethoven et ses trois styles (Beethoven and his Three Styles). Lenz proposed that Beethoven's creative output be marked by three periods of distinct stylistic personality and he identified specific compositions as milestones for each period. Lenz considers that the first period opens with the Piano Trios, Op. 1, and culminates with the performances in 1800 of his first symphony and Septet. The second period spans the period from the publication of his Moonlight Sonata to the Piano Sonata in E minor, Op. 90 in 1814. The last period covers Beethoven's works after Op. 90 to his death in 1827.

Although later scholars have called into question such a simplistic categorisation, it is still widely used. Extensive subsequent analytical consideration of Lenz's thesis has resulted in a slight revision of his original dates and broad consensus regarding Beethoven's three periods is as follows:

a formative period that extends to 1802 a middle period from 1802 to 1814, a late period from 1814 to 1827

Generally, each period demonstrates characteristic stylistic evolutions in Beethoven's musical language and preoccupations as well as important developments in the composer's personal life. For example, the middle period was ushered in by the 'Heiligenstadt Testament', a letter in which Beethoven, despairing about his hearing loss, considers and then rejects taking his life. On the other hand, the late period began with a period where Beethoven, suffering from the aftereffects of a myriad of personal and external crises, including the episode of the 'Immortal Beloved', struggled to compose for several years.

Early period Many of Beethoven's early works were not assigned an opus number and were simply listed with the label WoO, which is the abbreviation for the German term "works without opus number." Some, however, were published with opus numbers later on such as several compositions in the Eight Songs, op. 52. Although these were compiled between 1803 and 1805 and published in the latter year, were written during his early years in Vienna and Bonn.

The compositions that Beethoven wrote in his formative period can be generally characterized by the composer's efforts to master the predominant classical language of the period. His works from this period can be subdivided into two, based on the composer's residence. First, various juvenalia, written when the adolescent Beethoven was in residence in Bonn and heavily indebted to the works of contemporaries, especially Mozart and his teacher, Christian Gottlob Neefe. These early efforts can be seen in a set of three piano sonatas (WoO 47) and piano quartets (WoO 36) that Beethoven wrote before 1792. The Quartets, for instance, are each specifically modelled after three Violin Sonatas Mozart published in 1781 – K 296, 379 and 380 – and Beethoven would later draw upon this familiarity in the composition of several of his own Violin Sonatas.

Second, a number of more substantial and original works were written after Beethoven moved to Vienna and commenced studies with the famed Austrian composer and leading musical figure of the period, Joseph Haydn. As the 1790s progressed, his mastery of the Viennese style became increasingly clear, and his works became more and more experimental, especially in genres like the piano sonata. By the period 1798–1802, his piano sonatas had become increasingly more experimental, but his Op. 18 string quartets and 1st symphony are more conservative than the sonatas, probably a symptom of his relative inexperience in composing in these genres in comparison to the piano sonata.

Bonn period

With the exception of a visit to Vienna in 1787, Beethoven lived in Bonn until 1792, where he worked in the court chapel of the Elector of Cologne. His stints in the court chapel exposed him to a wide variety of musical style, not just from Vienna, but also from Venice and Rome. In addition to this, he played the viola in the orchestra of the Bonn Court Theatre from 1789, which exposed him to operas like Mozart's The Marriage of Figaro. Some forty compositions from this period are extant, including ten early works written by the young adolescent Beethoven when he was being promoted as a child prodigy performer and published as a result of the efforts of his teacher. It has been suggested that Beethoven largely abandoned composition between 1785 and 1790, possibly because his superiors in the palace chapel and court theatre did not compose music for the court, and thus not providing an example for the young Beethoven, and also because of negative critical reaction to his first published works. A 1784 review in Johann Nikolaus Forkel's influential Musikalischer Almanack compared Beethoven's efforts to those of rank beginners. Whatever the case, most of Beethoven's earliest surviving works were written after he turned twenty, between 1790 and 1792. Some of this music was later published by Beethoven, or incorporated into later works. As such, they provide an important foundation for judging the later evolution of his style.

Beethoven's early publications have been notable for scholars because of the view that it already indicated success as a child composer. One assessment stated that "if a child composer managed only a single published item, this might not indicate much, but if they had at least two publications, this is far more significant, for it suggests that the first one had had some success." Beethoven's childhood compositions had been published until 1784. An account cited how, by age thirteen, the child prodigy was already established, having composed three sonatas and four small works in addition to the earlier work called Dressler Variations. This is significant because, at this point, he no longer needed to be taught by a tutor, who would have influenced his musical style.

In general, Beethoven's earliest compositions show his struggles to master the prevailing classical style, both in structural and idiomatic terms. Several works, including two he later published, show the incipient signs of his later individual style: twelve Lieder, several of which he published in 1805 as Opus 52, his Wind Octet, later published as Opus 103, and several sets of Variations, including one (WoO 40) for violin and piano on Mozart's aria "Se vuol ballare" (later reworked in Vienna). Although these works largely conform to the formal conventions of the classical style, including strict observance of form and, in the variations, the decorative filigree associated with the genre, they also show early signs of Beethoven's later tendency to the more substantive treatment of thematic material.

Beethoven also produced numerous fragments of larger-scale works, including a symphonic movement (also written in C minor), a violin concerto, an oboe concerto, an early draft of his B-flat Piano concerto (both now vanished), and a concertante for piano, flute and bassoon. Scholars generally regard these early efforts as bland and uninspired and have concluded that his first efforts at writing in the classical sonata style (with the exception of his Wind Octet) were poorly conceived. Gustav Nottebohm, for example, wrote of Beethoven's Dressler Variations (WoO 63), "they show not a trace of contrapuntal independent part-writing. They are figural variations of the simplest kind".Nottebohm, Gustav (1873) Beethovens Studien. Leipzig & Winterthur. p. 10 Téodor de Wyzewa considered his early "Kurfürsten Sonatas" written in 1783 (WoO 47) as merely "correct imitations of Haydn.".Wyzewa, Téodor de (1914) Beethoven et Wagner. Paris. p. 44

The most ambitious work that Beethoven composed during his Bonn years was a funeral cantata to commemorate the death of Emperor Joseph II, commissioned by the literary society of Bonn. Though it was not performed, it was evidently impressive enough that Beethoven was commissioned to write a second cantata 'On the Accession of Leopold II to the Imperial Dignity', which was again not performed. These works already show skill in choral writing, as well as in writing arias, the latter also exhibited by three concert arias he composed around this time.

Considered as a whole, Beethoven's compositional efforts in Bonn demonstrate the importance of his move to Vienna in terms of the development of his musical style and the sophistication of his grasp of classical form and idiom, for his efforts in the sonata style are less accomplished than his efforts in other genres like variations, Lieder, and large vocal-orchestral pieces.

Early Vienna Period