Title: Three themes in the work of Charles Ehresmann: Local-to-global; Groupoids; Higher dimensions. Author: Ronald Brown Author's e-mail address: (Optional) Author's mailing address: Department of Mathematics, University of Wales, Bangor, Gwynedd LL57 1UT, UK. AMS classification number: 01A60,53C29,81Q70,22A22,55P15 Other useful information (such as arXive submission number): arXive math.DG/0602499 UWB Math Preprint 06.03 Expansion of an invited talk given to the 7th Conference on the Geometry and Topology of Manifolds: The Mathematical Legacy of Charles Ehresmann, Bedlewo 8.05.2005-15.05.2005 (Poland). Abstract: This paper illustrates the themes of the title in terms of: van Kampen type theorems for the fundamental groupoid; holonomy and monodromy groupoids; and higher homotopy groupoids. Interaction with work of the writer is explored. \footnote{KEYWORDS: Ehresmann, local-to-global; fundamental groupoid; van Kampen theorem; holonomy and monodromy; higher homotopy groupoids. \\ MSClass2000:}