A compactification is `wonderful' if the added locus is a normal crossing divisor. This term was motivated by Fulton and MacPherson's construction of a compactification X[n] of the configuration space of n distinct labeled points in a non-singular algebraic variety X (a smooth scheme if you like). Part I will mainly be an exposition of their results: an explicit description of degenerate configurations, the construction, the structure of the strata of the degenerate locus.