Alexander von Humboldt, who had never obtained a systematic and thorough education in natural sciences, and was in fact an autodidact in the field, made natural sciences the subject-matter of his creative research later on in his life. Humboldt's research was dominated by biological and geographical interests. There were roughly three periods, of about twenty years each, in his research activities. The first period, when Humboldt was still a young man, lasted until 1799, the year in which Humboldt embarked on his great American journey. The second period (1799-1834), covered the five-year-long journey (1799-1804), his return to Europe and the writing up of the research material that he had gathered during the journey, as well as the editing of the 'Voyage', completed in 1834. The third period was spent by Humboldt on writing the four volumes of the 'Cosmos'. Humboldts' research in the first period was devoted to diachronic causal regularities, investigated by means of the experimental method (e.g. electrophysiological research); in the second period, Humboldt focused his attention on synchronic morphological (coexistential) laws, which he studied using the descriptive-comparative and typological methods (e.g. phytogeographical studies); as for the third period, Humboldt's research interests dealt with attempts to produce an empirically-based theoretical synthesis of the knowledge about the Cosmos as a whole. Humboldt's research stance was always characterized by empiricism, a tendency to use a quantitative approach in his studies, and to present the results of his research in a visual manner; in the last two periods, Humboldt's methodology was dominated by a holistic approach. Humboldt combined a tendency towards giving a theoretical framework to his research with a negative attitude to the German romanticist natural philosophy (Naturphilosophie). The methodological analyses carried out in the current article lead to an image of Humboldt as scholar of the previous epoch - the Enlightenment.