This paper examines the literature on the use of crowdsourcing for speech-related tasks: speech acquisition, transcription and annotation as well as the assessment of speech technology. 29 papers were found, representing, 37 different experiments, which were annotated and analyzed to find trends in the field. The paper focuses on the different techniques used for quality control and the variety of sources of "crowds". Finally, we propose several challenges for the future of crowdsourcing for speech processing.