The INFIERI school aims at presenting some of the most exciting frontiers of physics and technology. The matter we know (baryonic matter made with protons, neutrons and electrons) is less than 5% of the energy content, and the Universe is dominated today by unknown Dark Energy (DE) and Dark Matter (DM). The existence of DM is now a mainstream concept, although at galactic scales all evidence for DM can also be explained by models with modified gravity. Evidence at large scales are however hard to reconcile with a simple modified gravity model. Cosmological Microwave Background (CMB) measurements show evidence for non-baryonic DM, which cannot be explained by the no-DM modified gravity models. Large scale N-body simulations prefer Cold Dark Matter (CDM) to Hot Dark Matter (HDM), Cold/Hot designating non-relativistic vs relativistic particles at decoupling, but the nature of DM is still unknown and many hypothesis have been suggested and explored. Some extensions of the Standard Model of Particle Physics expect particles which are neutral and interact very weakly with other forms of matter (WIMPs) In this short lecture notes, which is not aimed as a review of the field, I will summarize what is known about the existence of DM, which lead us to develop the most sensitive detectors in space, on Earth, and in underground laboratories. I will focus mainly on the Direct Detection of WIMPS and some of the experimental challenges. As the 2019 INFIERI school was held in Wuhan, China, I have mainly selected examples from the Chinese projects.