Troyanov, Marc2008-03-172008-03-172008-03-172003https://infoscience.epfl.ch/handle/20.500.14299/20138This is the text of an introductory lecture I made at the Séminaire Borel 2003 (IIIème Cycle Romand de Mathématiques). The general theme of that seminaire was Tangent Spaces of Metric Spaces.text::conference output::conference presentation