For many years tracing the timeline of the history of (primarily Western) philosophy was done in a distinction of 3 eras. More recently, some have proposed a 5-period timeline. Both of these arrangements of classifications had and have fuzzy and sliding dates for their borders as well as for the resulting proposed inclusion of figures and geographies in their respective classifications -- a certain arbitrariness is unavoidable. (Just be aware of this as you encounter philosophy books and are possibly confused by some ambiguity in scope and content suggested by the terms used in their respective titles and descriptions.)
For this guide, in informing you of some available philosophy eBook and print resources, we have adopted yet another proposed grouping, a commonly followed 4-era breakdown of classification. Boxes for Medieval Jewish philosophers, for Islamic philosophers and one for Eastern and other non-European philosophers have been added as supplementary representation of philosophical strands of thought across history. Each of those collective groups can be broken down into distinctions of time, geography, religious traditions and more. There is especially some overlap in assignment between the Islamic and Jewish philosophers designations and the (mostly Western) Medieval Period one. Note also that especially during the Medieval Period, as well as in the Ancient Period to some extent, there was often a very close connection between religious thought and philosophy. (No hierarchy between Western or non-Western is implied in this presentation.)