  Multiverse scenarios are common place in contemporary high energy physics and
cosmology, although many consider them simply as bold speculations. In any case
there is nothing like a single theory or a unified model of the multiverse.
Instead, there are innumerable theoretical proposals often reciprocally
incompatible. What is common to all these scenarios is the postulated existence
of many causally disjointed regions of space/time (if not completely separated
space-times) and the consideration of the observable universe as atypical in a
global perspective. This paper examines the history of modern cosmology
focusing on the forerunners of current ideas, and shows how some fundamental
issues tend to present themselves on increasingly deeper levels of physical
knowledge.
