Magnetically responsive soft nanoparticle systems are colloidal model systems where particle-particle interactions can be tuned through external magnetic fields. Macroscopic behaviour of soft nanosystems, depending on the size of magnetic nanoparticles degree of integration in the carrier fluid, varies from a magnetizable fluid continuum to a suspension of structuring magnetic particles.This book covers the most recent results in the field of magnetically responsive colloidal nanosystems, with special emphasis on engineering and biocompatible ferrofluids (bio-ferrofluids). It demonstrates the progress in remote controlled nanosystems, in particular in the field of magnetically controllable nanofluids.