In last couple posts in this series, we tied up the Renaissance period of music history, both in the secular and sacred genres. As we move into the Baroque, there is less distinction between the two, and they progress in basically the same direction, so you'll be hearing a lot less about the dichotomy between sacred and secular.
First off, let's examine the term "baroque." Today, it is simply used to describe various styles developed in the arts between 1600-1750(ish). However, it was originally applied to the time period as an epithet by 19th-century art critics, implying that one was wrinkling one's proper classical nose at the gaudy, overly ornamented style of visual art or music prevalent during this period in history. But, as I have been reminded three times in the past couple months by three different history professors, art history is not a linear progression: we are not moving from good to better to best. Each time period had its strengths and weaknesses, and those classical critics would have done well to remember that. Either way, "baroque" is no longer considered a derogatory term and you can use it safely without be arrested by the Politically Correct Police. (Such an organization exists, trust me. Especially on Facebook. They're kind of like the Grammar Nazis.)
If you recall, the Renaissance period finished with a bang, full of crazy dissonance, over-the-top dramatics, and elaborate text painting. Towards the end of the period, there was a group of intellectuals who called themselves the Florentine Camerata (Florence Club) that met regularly to discuss the state of the world, and more specifically that of the arts. One of them, Vincenzo Galilei (father of the more famous Galileo Galilei of gravity and heliocentrism), write a fairly complex treatise on the reasons why the popular music of the day was not as effective as the ancient musics. He also added his two-cents on how music should change for the betterment of society rather than its amusement.

This led, naturally, to a change in styles. Instead of focusing strongly on contrapuntal textures, Galilei argued for the use of monody, or compositions made up of one primary voice with harmonic accompaniment. This would bridge the gap between single line chants of the very ancient times and the multi-voiced polyphonic works of more recent styles.
Galilei's intellectual theories sparked a radical change in compositional practice, leading to the birth of the ubiquitous basso continuo line that persisted throughout the Baroque period and even somewhat into the Classical (Beethoven himself included a continuo line with figured bass in a few of his compositions). However, I've spent so much time talking about the theory that practice will have to wait till the next post. When that time comes, I'll start by defining the whole basso continuo idea, and then we'll move on to some of the seminal composers of the period.