As a basic principle relating to the assessment of damages for breach of contract common to all legal systems is that no damages are recoverable if the plaintiff has suffered no loss. In all systems loss is broadly defined to include any harm to the person or property of the plaintiff. The object of awarding damages for breach of contract is to put the aggrieved party into as good a financial position as that in which he would have been, had the defendant duly performed the contract. This process has been called compensating the aggrieved party for loss of his bargain. In the present article we have analysed the concept of loss and his kinds in the two main legal families (Civil Law and Common Law) as well as in the most important instruments of uniform law: Viena Convention on the International Sale of Goods of 11 April 1980, „UNIDROIT principles of international commercial contracts” and „Principles of the European Contract Law” worked out by the Commission for European Contract Law.