The transport, distribution and collisions of particles in turbulent flows is of fundamental interest, as well as being present in a variety of engineering and naturally occurring flows. Examples of related scientific challenges include rain formation in clouds, pollution dispersion in the atmosphere, emission reduction in combustion and plankton population dynamics. In such flows, particle inertia is an important parameter, but in many cases finite particle size and deformation play important roles. In most real life flows, the flow geometries are complex due to mixed forcing at various scales. This in addition to the complex relationship between large scale structures, intermittency and anisotropy at the small scales of motion in turbulence present us with a rare challenge increase the scope of our understanding, by systematically investigate complex flows from the numerical, theoretical and the experimental point of view.