For the first time in historiography, we represent a comparative study of the concept of active life as found in three European thinkers of the 15–16th centuries: Italian humanist Leonardo Bruni, Erasmus of Rotterdam and Jean Calvin. The study makes use of primary sources, including those not yet accessible to Russian-speaking readers, as well as of Russian and international historiography. We show that the apology of active life steadily increases from one thinker to another, turning into a forceful exhortation in J. Calvin. At the same time, the study discloses significant dissimilarities between L. Bruni’s, Erasmus’, and J. Calvin’s views of active life, which is explained by the fact that the three thinkers lived in different epochs of European history. Besides that, the attitude of each of the authors to the opposite of active life, i. e. the contemplative life, is examined, showing that each author had his own understanding of the latter. In the fact that each thinker prefers active life to the contemplative, as well as in the increase in the apology of active life from L. Bruni to Erasmus and then to J. Calvin we see a reflection of the transition from the “era of contemplative life” to the “era of active life”, which took place in Europe during the Renaissance and Reformation.