An improved understanding and ability to simulate the transport and fate of natural colloids, colloid-associated contaminants, microorganisms, and engineered nanoparticles in porous media is needed for a wide variety of applications, including: risk assessment, remediation operations, wastewater treatment, and well production. For this session we invite submissions that describe experimental, theoretical, and modeling research related to these topics. Areas of special interest include: 1) novel experimental approaches; 2) studies designed to quantify the fundamental physics, chemistry, and/or biology influencing transport and fate; 3) improved mathematical models and computational approaches; and 4) studies and observations at scales from pore-scale to watershed.