Acoustic emissions of animals serve communicative purposes and most often contain species-specific and individual information exploitable to listeners, rendering bioacoustics predestined for biodiversity monitoring in visually inaccessible habitats. The physics of sound define the corner stones of this communicative framework, which is employed by animal groups from insects to mammals, of which examples of vocalisations are presented. Recording bioacoustic signals allows reproducible identification and documentation of species' occurrences, but it requires technical prerequisites and behavioural precautions that are summarized. The storing, visualizing and analysing of sound recordings is illustrated and major software tools are shortly  outlined. Finally, different approaches to bioacoustic monitoring are described, tips for setting up an acoustic inventory are compiled and a key for procedural advancement and a checklist to successful recording are given. Extensive literature and reference to a collection of web resources (http://www.bioacoustics.myspecies.info) complete the text.