The debate about how far the Moon causes biological effects has continued for two millennia. Pliny the Elder argued for lunar power “penetrating all things”, including plants, fish, animals and humans. He also linked the Moon with tides, confirmed mathematically by Newton. A review of modern studies of biological effects, especially from plants and animals, confirms the pervasive nature of this lunar force. However calculations from physics and other arguments refute the supposed mechanisms of gravity and light. Recent space exploration allows a new approach with evidence of electromagnetic fields associated with the Earth’s magnetotail at full moon during the night, and similar, but more limited, effects from the Moon’s wake on the magnetosphere at new moon during the day. The disturbance of the magnetotail is perhaps shown by measurements of electric fields of up to 16 V/m compared with the usual <1 V/m, suggesting the possibility of weak biological effects on some sensitive organisms. Similar intensities found in sferics, geomagnetic storms, aurora disturbance, sensations of a ‘presence’ and pre-seismic electromagnetic radiation are known to affect animals and 10–20% of the human population. There is now evidence for mechanisms such as calcium flux, melatonin disruption, magnetite and cryptochromes. Both environmental and receptor variations explain confounding factors and inconsistencies in the evidence. Electromagnetic effects might also account for some evolutionary changes. Further research on lunar biological effects, such as acute myocardial infarction, could help the development of strategies to reduce adverse effects for people sensitive to geomagnetic disturbance.