Exercise capacity is a powerful predictor of mortality and physical activity is known to help prevent a wide range of non-communicable diseases. That these benefits might be mediated by secreted products of skeletal muscle is an attractive hypothesis, since it raises the possibility that such products might be manipulated for therapeutic gain. Myokines are peptides or proteins expressed and released from skeletal muscle in order to carry out endocrine or paracrine functions. Since the serendipitous discovery of Interleukin-6 as the first labelled myokine, attempts have been made to uncover a wider myokinome. However, myokine discovery is challenging and unbiased, ‘omic’ approaches are hampered by considerable technical hurdles such as large dynamic ranges of protein abundance in skeletal muscle and plasma. Despite this, novel candidate myokines have been identified which might partially explain the preventative influence of exercise on metabolic disease and breast cancer. Here, a selection myokine discovery approaches will be presented involving proteomic screening of skeletal muscle and plasma in rodent and human models of exercise. Approaches to the functional validation of myokine candidates, involving the use of CRISPR/cas9 genetic manipulation, transfusion and parabiosis in mice will also be discussed.