Fluorescence microscopy is widely used for chemical imaging of intrinsically fluorescent chemical species, such as chlorophylls or nonfluorescent species (e.g., DNA) that have been labeled appropriately or to which a relevant molecular probe has been added. However, there are numerous analytes that neither have an intrinsic luminescence nor can be rendered luminescent with the help of labels or probes. Such parameters include oxygen, pH, CO2, ammonia, and glucose. There are also numerous applications where the 2D distribution of a chemical or physical parameter is of interest. The use of a "sensor paint" is ideal in such situations. The state of this new technology is discussed herein with emphasis on current and future trends, for example, the use of pressure- and temperature-sensitive paints; known technological limitations are also discussed. These "paints" respond to a (bio) chemical parameter with a change in their optical properties. The object of interest is painted and the color or fluorescence of the paint is monitored by optical imaging. This technique enables monitoring of physical and chemical parameters over relatively large,areas and in real time.