A waste heat recovery system, comprising: a) an internal combustion engine for supplying a high grade waste heat thermal resource fluid and a low grade waste heat thermal resource fluid; b) an intermediate thermal cycle arranged to vaporize water as an intermediate fluid by means of said high grade waste heat thermal resource fluid and to expand the intermediate fluid within a first turbine, whereby to produce power; and c) an organic thermal cycle arranged to: preheat an organic motive fluid by means of said low grade waste heat thermal resource fluid; vaporize the organic motive fluid by means of the discharge of said intermediate fluid from said first turbine, and expand the vaporized organic motive fluid in a second turbine, whereby power is produced; d) a combined condenser-vaporizer unit (CVU) for vaporizing the organic motive fluid and condensing the intermediate fluid, the CVU arranged such that the intermediate fluid from the first turbine is brought into heat exchange relation with the preheated organic motive fluid; wherein the system is arranged such that the condensed intermediate fluid is brought in heat exchanger relation with the high grade thermal resource fluid at a boiler (15, 75) and is vaporized thereby to produce steam; wherein the boiler comprises a first stage boiler and a second stage boiler; and wherein the system is arranged such that the condensed intermediate fluid exits the CVU via first and second conduits (16, 76) extending to the first and second stage boilers (15, 75), respectively, the high grade thermal resource fluid exiting the internal combustion engine being delivered to the first stage boiler to generate high pressure intermediate fluid for supply to the first turbine and the high grade thermal resource fluid exiting the first stage boiler being delivered to the second stage boiler to generate low pressure intermediate fluid for supply to the CVU. a) an internal combustion engine for supplying a high grade waste heat thermal resource fluid and a low grade waste heat thermal resource fluid; b) an intermediate thermal cycle arranged to vaporize water as an intermediate fluid by means of said high grade waste heat thermal resource fluid and to expand the intermediate fluid within a first turbine, whereby to produce power; and c) an organic thermal cycle arranged to: preheat an organic motive fluid by means of said low grade waste heat thermal resource fluid; vaporize the organic motive fluid by means of the discharge of said intermediate fluid from said first turbine, and expand the vaporized organic motive fluid in a second turbine, whereby power is produced; preheat an organic motive fluid by means of said low grade waste heat thermal resource fluid; vaporize the organic motive fluid by means of the discharge of said intermediate fluid from said first turbine, and expand the vaporized organic motive fluid in a second turbine, whereby power is produced; d) a combined condenser-vaporizer unit (CVU) for vaporizing the organic motive fluid and condensing the intermediate fluid, the CVU arranged such that the intermediate fluid from the first turbine is brought into heat exchange relation with the preheated organic motive fluid; wherein the system is arranged such that the condensed intermediate fluid is brought in heat exchanger relation with the high grade thermal resource fluid at a boiler (15, 75) and is vaporized thereby to produce steam; wherein the boiler comprises a first stage boiler and a second stage boiler; and wherein the system is arranged such that the condensed intermediate fluid exits the CVU via first and second conduits (16, 76) extending to the first and second stage boilers (15, 75), respectively, the high grade thermal resource fluid exiting the internal combustion engine being delivered to the first stage boiler to generate high pressure intermediate fluid for supply to the first turbine and the high grade thermal resource fluid exiting the first stage boiler being delivered to the second stage boiler to generate low pressure intermediate fluid for supply to the CVU.