Knowledge workers who want to apply knowledge visualization have to determine which visual representation and thereupon which visualization tool is suitable for their needs. To support knowledge workers in this sophisticated problem a systematic approach is presented that matches typical tasks in knowledge management to visualizationtechniques that support these tasks. Knowledge workers are provided with a three-dimensional decision matrix that enables them to identify a suitable visualization technique for a certain knowledge problem. To be able to systematically evaluate and identify adequate visualization techniques a set of evaluation criteria is introduced.