Superconductivity is an instability of a normal state, and the understanding of the origin of the normal state out of which high-temperature superconductivity evolves is therefore crucially important. There are numerous experimental evidences that point to a rich and unusual physics of the normal state of the underdoped cuprates. The most significant observations are:
i) Mysterious supression of the electron spectral weight in the underdoped regime (the pseudogap phase);
ii) Abrupt destruction of the long-range antiferromagnetic phase at a suprisingly low doping level;
iii) Large vs small Fermi surface crossing in the underdoped cuprates.
All these properties indicate that the relevant normal state displays a non-Fermi liquid behaviour which clearly rules out the standard BCS paradigm. Despite the intensive work over a few decades there is still a lack of a reliable theory to account for all these data. In the present talk I show that the driven force behind the unusual physics of the underdoped cuprates is strong electron correlations.