CD Projekt RED has announced that The Witcher series has shipped 5M units in the series. A little investigation finds that the series has actually sold 1.76M units.
According to VGChartz, The Witcher sold 350K - including the original and Enhanced versions that were released on PC, while The Witcher 2 sold 800K units on PC and the Xbox 360 sold 600K.
The Witcher 3: Wild Hunt was announced this week for 2014 for PC.