This document discusses three case studies that demonstrate the usefulness of knowledge organization systems (KOS) in information retrieval applications. The case studies show that: 1) Controlled vocabulary searches using term mappings between domains improved search effectiveness compared to searches without mappings. 2) Query expansion using recommendations from discipline-specific search term recommendation services led to better search results than using a general recommendation service. 3) Usage of search term recommendations in an interactive IR system was found to positively correlate with successful search outcomes in subsequent search steps.