This paper explores the continuous inertial focusing, ordering, and separation of particles in microchannels under laminar flow conditions. The authors observe that particles migrate across streamlines in a predictable and accurate manner due to lift forces, which become significant when inertial aspects of the flow are important. They identify symmetric and asymmetric channel geometries that enhance these inertial forces, creating continuous streams of ordered particles in three spatial dimensions. The ordering is lateral within the transverse plane and longitudinal along the flow direction, with a fourth dimension of rotational alignment observed for discoidal red blood cells. The process is independent of particle buoyant direction, suggesting minor centrifugal contributions. Theoretical analysis indicates that these principles are operational over a range of channel and particle length scales. The ability to differentially order particles of various sizes, at high rates, and without external forces has broad applications in continuous bioparticle separation, high-throughput cytometry, and large-scale filtration systems.This paper explores the continuous inertial focusing, ordering, and separation of particles in microchannels under laminar flow conditions. The authors observe that particles migrate across streamlines in a predictable and accurate manner due to lift forces, which become significant when inertial aspects of the flow are important. They identify symmetric and asymmetric channel geometries that enhance these inertial forces, creating continuous streams of ordered particles in three spatial dimensions. The ordering is lateral within the transverse plane and longitudinal along the flow direction, with a fourth dimension of rotational alignment observed for discoidal red blood cells. The process is independent of particle buoyant direction, suggesting minor centrifugal contributions. Theoretical analysis indicates that these principles are operational over a range of channel and particle length scales. The ability to differentially order particles of various sizes, at high rates, and without external forces has broad applications in continuous bioparticle separation, high-throughput cytometry, and large-scale filtration systems.