What is now referred to as the Ramsden v Dyson principle began life as nothing more than a bundle of instances in which equity would assert jurisdiction. It experienced a period of systematisation in the later years of last century when attempts were made to encumber it with a series of rules. In the middle years of the present century, with Lord Denning taking the lead, the Ramsden v Dyson principle quickly shed these rules and took on the wider function of providing the courts with a weapon whereby non contractual expectations may be fulfilled, or otherwise protected. The basis upon which the courts determine whether the expectation will be fulfilled is whether or not it would be unconscionable to the representee to allow the expectation to remain unfulfilled. This will normally involve some degree of detriment to the representee if the representor is permitted to resile from the expectation which he has raised in the mind of the representee. Thus in order to succeed in invoking the Ramsden v Dyson principle the representee has to show the existence of two basic requirements. Firstly, that the other party, the representor that is, has raised an expectation which would be such to influence a reasonable man. Secondly that it would be unconscionable for the expectation not to be fulfilled. The present state of the law allows virtually a complete discretion to the courts as to when they will assert jurisdiction and as to the remedy which will be decreed. The remedy is not limited to a simple specific performance of the expectation. The basis of the Ramsden v Dyson principle is barely distinguishable from that underlying other heads of estoppel such as the High Trees principle and the Dillwyn v Llewelyn principle. With the departure of Lord Denning M.R. from the judicial scene a degree of momentum has apparently been removed from the development of the principle and there have been signs in some recent cases of attempts to limit the further development of the principle. The method of investigation has been by orthodox case analysis with the division of the work following from the judicial decisions.