Baroque Music in general is defined as "music written and performed between 1600 and 1750". As this is an overly long period of time, musicologists tend to split it up:
- Early baroque: from 1600 to 1670, containing early opera, simple choral arranging and small ensembles.
- Middle baroque: from ca. 1670 to 1720, heavily influenced by French ceremonial music and the rule of Louis XIV.
- Late baroque: In short, the age of Johann Sebastian Bach and Georg Friedrich Händel. Lots of pomp, great choruses and awesome musical effects.
Because of the long span, the term has no clear border, either to the Renaissance or to the classical era: Late Renaissance music lived on and prospered for years, along with the musical tropes in question, all the way to 1660, while early classical tropes were well on the way in the last decade of Bach, when even he was considered old and out of fashion. So the years set are there mostly for convenience. Note that individual composers can be assigned to more than one period if they were adaptable and lived long enough; the incredibly productive and versatile Georg Philipp Telemann (1681-1767) for instance represents Middle and Late Baroque as well as Early Classicism. Baroque tropes surfaced in fact in the late Renaissance, as early as 1570, in an era called mannerism. This covered visual art, literature and music, and was the Sturm und Drang period of the Renaissance.
Early Baroque Music: Lots and lots of weird instruments.
The beginning of the baroque era tends to be placed in renaissance Venice, where the local lords, and the duke, hired a lot of musicians from 1560 and onwards. Here, some experimenting took place, and the composers of the day discussed how to revive the music of the classical period, which in this case meant Ancient Greece. Madrigals were the craze of the day and had been for years, but the style had been gradually more elaborate, and the combination of madrigals into a longer story with solo singing in between resulted in a new genre: the musical drama, or to be precise: the opera. The early operas snatched their plotlines from Greek myth, or roman myths, and a lot of the stories were remakes of the classical texts. They seemed to be rather fond of Orpheus, as he was set to music several times over the years. The first surviving opera casts him in the leading role, with a happy ending nonetheless. The composer? Claudio Monteverdi, who couples as both a renaissance and a baroque composer. His fifth book of madrigals is often seen as a starting point for a new expressiveness (although this had been in making for years already).
The music of the era saw a gradual shift from vocal style (madrigal) to instrumental styles, and instruments evolved immensely over the years. Thus, a new and practical instrument was developed to suit the fancies of a new generation: the violin, who gained its modern shape almost at the right time. From this point and ever since, orchestral music grew, and so did the volume. Beethoven may have broken the first sound barrier, but the foundation for his instruments were laid 200 years prior to his time. The shift is apparent in the development of the general bass line, setting up the first system of chords over a written bass. This principle is a valuable and necessary ingredient in all popular music.
Apart from the violin, brass instruments had the upper ground. And it is fair to say that every group played separately for most of the time, as the difference in volume was immense.
Every "family" of musical instrument was based on the choral principle, with four pitches: descant, alto, tenor and bass. The violin groups are still ordered this way. So is the brass section. But the wood instruments? Let's just say that this part of instrumentation is plain weird from a modern point of view. Recorders alone could be found in six different sizes, and then you had the racketts, a somewhat close relation to the modern oboe, sounding like a goat. Four racketts at the same time sounds even more interesting. And then there is the krummhorn, sounding like this (Ok: they are labeled as renaissance instruments, but they were definitely in use in the early baroque).
On the fiddle side, you had the gamba, and among other string instruments, we find the lute. It is fair to say that this era is the drooling spot for any early music nerd. Fiddles were also made with sympathetic strings, a trait which came to survive in the most unlikely places.
Instruments aside, the era produced two different modes, the first practice, derived from the renaissance, based on vocal forms, and then the second practice, based on the new instrumental ones. Not surprisingly, this practice leaned heavily on the contemporary dance music. This became the starting point for almost every instrumental form achievable the next hundred years. Much of the instrumental music had strong rhythm, and was part of an elaborate pattern of dances, usually put together in a suite. In time, this was refined into music for listening, and even the symphony seems to have its roots in this pattern. To give an example of what the instrumentalists at the time were up to, listen to this!
The middle Baroque era: Here comes the sun king
The music of the time was often incited by patrons, often princes of some wealth. But the times were also turbulent, and the golden age of baroque didn't occur until things settled down. And this happened with the establishment of absolutism, and the rule of Louis XIV. His time also established the ballet as art form, and the dancers got style like never before. In those years, the greater body of music tended to be made in France, but the style was still Italian. Jean Baptiste Lully, the most known composer of this period, was an Italian born Frenchman, in service of king Louis. More peaceful times made the orchestras bigger, and the weirdest instruments were scrapped. The more known instruments surfaced, and we still use them today: The oboe, and the trombone. Trumpets and horns still had to cope with natural intervals, but valves were developed slowly. Horns and trumpets without valves were in use all the way up to Bach, who wrote much of his trumpet music for valveless instruments.
Outside France, the Italians were finding new forms, and the greatest inventor of them all, Antonio Vivaldi, together with some others, came to shape the nature of chords to an extent that modern popular music still is using his chord patterns.
Meanwhile in the Holy Roman Empire, which up until then had been considered a bit of a musical backwater, a new generation of composers sprang up that began to compete with French and Italian composers on at least equal terms and set the stage for Germany becoming a dominant force in European music for the next two centuries. The most three most prominent names were of course Bach, Händel and Telemann. A lot of this music was written for major and minor German courts, but there also evolved a more bourgeois music scene in the larger mercantile cities. Here public concerts and commercial opera houses were set up that were not paid for by wealthy patrons but by the tickets sold to the audience, and composers would add to their income by selling librettos to their oratorios to the audience or having their music printed and selling it to subscribers all over Germany and Europe. And the town fathers managed to entice some of the greatest names in music away from princely courts by giving them a secure position as directors of church music, as happened with Telemann (first in Frankfurt, then Hamburg) and Bach (at St. Thomas's church in Leipzig).
Apart from France, Italy, and Germany, the main composer of the period was Henry Purcell, who defined the musical style for Britain under the late Stuart kings. Unfortunately, he died before he passed 30, in 1692, and the torch was passed on to a German gentleman who came to England during the reign of king George I. His name was Georg Friedrich Händel (after moving to England, he anglicized the name to "George Frideric Handel"), and he was heavily influenced by Italian style and genres, and a self-promoting badass in many respects. Having previously worked at the opera in Hamburg, he took to the more modern and commercial ways of the music scene in London like a duck to water.
The late baroque: Bigger is better.
Not surprisingly, the late period came to be known as the era of Händel and Bach in later years, even if their contemporaries actually held Telemann in higher regard. At the same time, and at the time king Louis XIV in France died (at long last in 1715), people saw a shift in musical style, and more easy-going music. These new styles, called "sensitive style" in Germany and "regency style" in France (after the regent of the child king Louis XV), corresponded to the change in art and architecture from Baroque to Rococo and were precursors for the slowly emerging "classical style".
The opera, who had been serious business up till then, often staging pure tragedy and high romance, started to take in more commonplace characters, and the comic opera evolved. Furthermore, from being pure Italian stuff, the opera was suddenly performed in the common language. Italian survived as the main language of opera, both in the comic and the tragic subgenre, though, even though French continued to be used as well, and German was at least used for the usually more comic Singspiele.
As an afterthought: The split between comic and tragic opera led in turn to near streetfights in Paris, but that happened after 1750.
But as the eighteenth century marched on, the Italian opera fell out of fashion, especially in England, where Händel went on to write oratorios instead. Many of them are still on the classical hit parade. In Germany Bach, who never wrote any operas, concentrated his efforts on church music and secular music alike, and produced enough music for a lifetime of studies. But he also produced a number of sons, who in their turn became composers. And more than one of those denounced their father as the new styles emerged. Bach's music became neglected for hundred years, and studied solely by scholars. Even so, Wolfgang Amadeus Mozart owes much of his style to Vivaldi and Bach, especially in his last, and unfinished, requiem.
It is convenient to say that the Baroque era died with Bach. The year he died, 1750, saw the debut of a then 20 year old composer with a brand new idea for the use of strings. His name was Joseph Haydn, but he belongs to another story.
It's also probably worth noting that, although you'll invariably find Baroque music on the "Classical Music" shelf at your local record store, the Insistent Terminology of music scholars distinguishes between "Classical" as a broad genre category, and the Classical Period, which is what came after the Baroque era. That's why it can be a mild Fandom-Enraging Misconception to say, for instance, that Johann Sebastian Bach wrote classical music. As the saying goes, "If it's not Baroque, don't fix it."