The geological age in which life is hidden in the fossil record. It is opposite to the Phanerozoic Aeon, in which fossils are very clear. The name comes from the Greek for "hidden life". It lasted from the beginning of the Earth about 4500 million years ago until the beginning of the Cambrian Period about 570 million years ago. The Cryptozoic is also called the Precambrian.

The Cryptozoic Aeon is divided into three parts: the Hadean Era until about 3800 million years ago, then the Archaean Era until about 2600 million years ago, then the longest era, the Proterozoic.

The names Azoic for the earliest era and Archaeozoic for the Archaean have also been used. Sometimes the Cryptozoic is defined to mean the time before the Proterozoic.

Animals that live hidden in dark places like soil are also called cryptozoic.