Book excerpt: Design and operation of Janus particles have a great potential for applications in fields such as environmental remediation, electronic engineering, bio-imaging, bio-sensing, drug delivery and other biomedical tasks. Current research aims to imitate the molecular motors of biological systems by creating micro- and nano-scale particles which can exploit chemical energy so as to produce directional motion. The assembling of self-propelled particles and their movement can be controlled by using external fields, especially magnetic fields. The book references 332 original resources and includes their direct web link for in-depth reading. Keywords: Janus Particles, Bio-imaging, Bio-sensing, Drug Delivery, Environmental Remediation, Electronic Engineering, Asymmetrical Colloidal Particles, Catalysis-propelled Particles , Nanoscale Engines, Chemical Asymmetry, Self-propulsion, Diffusiophoresis, Electrophoresis, Thermophoresis, Bubble Generation, External Propulsion, Radiation Effects, Electric Field, Magnetic Field, Gravitaxis, Barrier Effects.