Books
Lawinenkunde by Stephan Harvey, Hansueli Rhyner and Jürg Schweizer
an ideal introduction to the subject.
PowderGuide: Avalanches: Risk - Check for Freeriders
THE German-language work for applied avalanche knowledge.
3x3 Avalanches by Werner Munter
THE classic. Now partly outdated. The basis of common risk management methods such as Stop or Go or SnowCard.
Lawinen: Verstehen - Vermeiden - Praxistipps by Eike Roth
as an introduction to the more complex world and basic research on avalanches
Lawine. Die 10 entscheidenden Gefahrenmuster erkennen von Rudi Mair & Patrick Nairz
Explains more the causes than the basics, good supplement.