This book constitutes the thoroughly refereed post-workshop proceedingsof the Workshop on Controlled Natural Language, CNL 2009, held inMarettimo Island, Italy, in June 2009.The 16 revised full papers presented together with 1 invited lecturewere carefully reviewed and selected during two rounds of reviewing andimprovement from 31 initial submissions. The papers are roughly dividedinto the two groups language aspects and tools and applications. Notethat some papers fall actually into both groups: using a controllednatural language in an application domain often requires domain-specificlanguage features.