We give an introduction to interferometrical concepts and their applicability
to Be stars. The first part of the paper concentrates on a short historic
overview and basic principles of two-beam interferometric observations. In the
second part, the VLTI/MIDI instrument is introduced and its first results on Be
stars, obtained on alpha Ara and delta Cen, are outlined.Comment: To appear in proceedings of the Astronomische Gesellshaft meeting,
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