This lecture was designed as an introduction to Plato's theory of Forms. Reference is made to key passages of Plato's dialogues, but no guidance on further reading is offered, and numerous controversies about the theory's interpretation are left in the background. An initial sketch of the theory's origins in the inquiries of Plato's teacher Socrates is followed by an explanation of the Forms’ primary characteristic, Plato's metaphysical separation of them from the sensible world. Other aspects discussed include the Forms’ metaphysical relation to sensible particulars, their ‘self-predication’, and the range of items that have Forms. Finally, the envisaged structure of the world of Forms is illustrated by a look at Plato's famous Cave simile.