Acoustic particle detection techniques have experienced a strong revival during the last few years, but are still in an R&D phase. Progress has been made since ARENA2005 a year ago in particular in simulation techniques for particle energy deposition, sound generation and propagation as well as detector response. Also new signal processing and reconstruction techniques have been reported. Recent in-situ measurements allowed to study available transducers in natural environments. Several projects, to be realized during the next years, aim to deliver the basic input for future arrays of ~100 km³ size. To study successfully highest energy cosmic neutrinos such arrays should use hybrid detection techniques, with optical, radio and acoustic sensors as basic elements.