Difficulties associated with quantum mechanics and traditional Copenhagen interpretation are discussed here. The most commonly accepted Copenhagen interpretation of quantum mechanics with it's physical and philosophical implications are described here. We concentrate on measurement problem and the relations of reality and quantum mechanics. In the second part we describe Einstein's opinions about Copenhagen interpretation of quantum mechanics, which are demonstrate by famous EPR paradox. We offer Bohr's answer to Einstein's objections with some historical facts about their long dispute. The third part of the article is brief description of fundamentals of hidden variables theories. Two famous no-hidden-variables theorems - von Neuman's proof and Bell's inequalities - are mentioned. Violation of the Bell's inequalities by quantum mechanics is proven here. We review actual status of Copenhagen interpretation and notice some other theories, which could replace this interpretation or quantum mechanics itself.