High spectral resolution X-ray spectra of cores of galaxy clusters shows little evidence for the cool X-ray emitting gas expected in the absence of heating. This is believed to be due to feedback by the central supermassive black hole. The spatial distribution and mass of such gas can help us understand feedback, and constrain the amount of matter which can form stars. By using high spatial resolution imaging of the Perseus cluster we can image cool X-ray emitting gas in filaments. I compare what we learn here with data at other wavelengths. In the second part of my talk I will discuss some limits on cold X-ray emitting gas obtained with deep observations by the RGS instrument on XMM-Newton in nearby clusters.