Particle agglomeration is concerned with how particles collide and adhere to each other in a fluid, thus forming larger structures called "aggregates". Depending on the field of research, particle agglomeration is also referred to as aggregation (for solid materials), coalescence (for droplets/bubbles), coagulation (non-Newtonian fluids) or floculation (polymers).

The usual measure is the mean aggregate size in suspension at a given time.

Particles aggregation has implications in a wide range of situations, including environmental & industrial applications such as:
   + Silt agglomeration leading to the formation of river deltas in geomorphology
   + Droplet growth within clouds in meteorology
   + Growth of planetoids in astrophysics
   + Flocculation of impurities in waster-water treatment facilities.

A particle agglomerate with another one in a two-step process:
   + the two particles are first brought in close proximity by the fluid (transport step);
   + particles can stick together if particle-particle interactions do not prevent it (attachment step).