Colloid chemistry is the oldest branch of chemistry predating even alchemy. However, the knowledge base of colloid chemistry began to fade from the chemistry curriculum and has only recently had a resurgence due to the importance of nanoparticles. The importance of the basic science of colloid chemistry will be briefly reviewed. Optical experiments (absorption, fluorescence, time-resolved fluorescence, dynamic light scattering etc.) can now be used to elucidate the surface coverage and electrostatic properties of nanoparticles. Colloids and colloidal principles are widespread in daily life, in nature and technical application. Why is milk white and some tooth pastes transparent? What are colloids and what is their behavior? Colloids are mixtures of different phases and diverse and complex appearance. What can we expect of such systems, how can we use their properties and how can we use their properties. With lots of examples from the daily life in the area of materials and of food, with key experiments, this lecture concerns the interdisciplinary and very broad topic of the colloids.