Dense active suspensions, such as those formed by swarming bacteria, constitute a type of active matter that is particularly hard to model.

Experimental techniques have demonstrated the ability to alter the collective dynamics of active systems with various types of external perturbations.

Some collective states in active matter exhibit topological properties through the formation of vortices and defects. In some living systems, defects have been shown to have important biological functions.

The dynamics of the sperm flagellum has been recently studied with particular attention to its fluctuations. It has been found that the precision of the flagellar beating is close to that of an individual dynein motor powering its motion, which in turn is close to the bound dictated by the thermodynamic uncertainty relation.

Active field theories are widely used to study collective effects in driven systems at all levels of organisation, allowing instabilities to pattern formation to be identified.

While active matter theory has successfully advanced our understanding of the collective dynamics resulting from individual sources of activity, multiple active processes usually act in concert in real biological systems.