  We review `particle partitioning entanglement' for itinerant many-particle
systems. This is defined as the entanglement between two subsets of particles
making up the system. We identify generic features and mechanisms of particle
entanglement that are valid over whole classes of itinerant quantum systems. We
formulate the general structure of particle entanglement in many-fermion ground
states, analogous to the `area law' for the more usually studied entanglement
between spatial regions. Basic properties of particle entanglement are first
elucidated by considering relatively simple itinerant models. We then review
particle-partitioning entanglement in quantum states with more intricate
physics, such as anyonic models and quantum Hall states.
