Humanism was a movement in early Renaissance Europe towards the revival of classical learning. The movement originated in Italy and can be traced back to at least as early as the thirteenth century. In the early stages of the movement the centre of humanist learning was Padua rather than Florence, but Florentines became dominant in the movement. Perhaps the most famous humanist, Petrarch, was from Florence though he did not live in the city.
Standard explanations of the rise of the movement stress the economic and political development of the Italian city states, which went through a phase of republican rule. The cities had a practical demand for classically educated scholars to both man their civil services and to educate the ruling class. This coincided with the beginnings of nationalist feeling in the cities, support for which was provided by the humanists' examination of ancient Roman history.
As Kristeller points out, humanism should not be equated with Renaissance thought in general. It is rather a specific movement within the overall Renaissance. As its name suggests, humanism was limited to the humanities - leaving out the natural sciences but also philosophy apart from ethics. The most important disciplines that the humanists worked in were grammar, rhetoric, poetry, history and moral philosophy.
The humanists collected ancient Roman and Greek texts, and translated a lot of Greek philosophy and literature into Latin, which was the language the educated public was more familiar with. The increased availability of ancient texts was an important aspect in the revival of classical learning championed by the humanists. But as Nauert points out, classical texts were available to medieval Europeans, especially after the Fourth Crusade had conquered Constantinople. So perhaps the renewed interest in seeking out classical texts rather than their availability is what should be emphasized when considering the humanist movement. But Kristeller, for instance, stresses that many texts were now available for the first time. I think this is an interesting point of interpretation - was the crucial factor the increased availability of texts or the increased interest in such texts?
Professionally, the humanists were active in education and also in state service. The humanists were dominant in secondary schools, where they taught classical Latin and Greek. They also had an influence in the universities. The educational role of the humanists also had a political aspect - they trained the ruling classes of the Italian city states, imparting to them the values of classical antiquity. Furthermore, the humanists took part in politics themselves, as they served the Italian city-states of the period as civil servants. Some also found employment in the papal administration.
The literary output of the humanists was characterized by a conscious imitation of classical authors. The humanists idolized the writers of antiquity and followed them in their style of composition and their vocabulary. However, the humanists added a kind of individualism that was absent from the authors of ancient Greece and Rome. Their writings have a sense of subjectivity - they take their own personal feelings, experiences, and opinions seriously. Naturally, then, the dominant literary genres in the humanist movement were the invective, the dialogue, the speech, the letter and the essay.
Finally, I think the relationship of humanism with philosophy is worth considering. The humanists were predominantly philologists, not philosophers. Petrarch, for instance, wrote only one treatise explicitly on philosophy. He did not produce an overall philosophical synthesis. However, it seems undeniable that humanists had a considerable influence on philosophy. Individual humanists contributed to logic and aesthetic theory. But more importantly, the humanists made the sources of ancient philosophy available by translating them. In the middle ages, Aristotle was the philosophical authority; the work of the humanists opened up alternatives to Aristotle by publishing the works of the Stoics, Epicureans and sceptics. Kristeller suggests that the humanists also had an important influence on the style of philosophical writing, for instance starting a revival of the philosophical dialogue.
The relationship of humanism with philosophy again raises more general questions about historical causation. To what extent can humanism be seen as having an important influence on philosophy regardless of the relatively little explicitly philosophical material produced by the humanists? If humanism did have a general influence on philosophy, how can this be defined precisely, in order to avoid airy generalizations? I think these are questions worth considering when thinking about the specific relationship of humanism with philosophy and the more general question of the influence and importance of humanism within Renaissance thought.
Mann, N. 'The Origins of Humanism' in Kraye, J. (ed.), The Cambridge Companion to Humanism, Cambridge, Cambridge University Press, 1996, pp. 1-19.
Nauert, C. G., Humanism and the Culture of Renaissance Europe, Cambridge, Cambridge University Press, 1995.
Kristeller, O., 'Humanism' in Schmitt, C.B. & Skinner, Q.R.D., The Cambridge History of Renaissance Philosophy, Cambridge, Cambridge University Press, 1988.