and shape of the molecules involved. This potential complication has been given an argument against the use of one of fluorescence recovery after photobleaching (FRAP) to determine bilayer diffusion coefficients. In a typical FRAP experiment a small (~30 µm diameter) area is photobleached by exposure to an intense light source. This area is then monitored over time as the “dead” dye molecules diffuse out and are replaced by intact dye molecules from the surrounding bilayer. By fitting this recovery curve it is possible to calculate the diffusion coefficient of the bilayer. An argument against the use of this technique is that what is actually being studied is the diffusion of the dye, not the lipid. While correct, this distinction is not always important, since the mobility of the dye is often dominated by the mobility of the bilayer. In traditional fluorescence microscopy the resolution has been limited to approximately half the wavelength of the light used. Through the use of confocal microscopy and image processing this limit can be extended, but typically not much below 100 nanometers, which is much smaller than a typical cell but much larger than the thickness of a lipid bilayer. More recently, advanced microscopy methods have allowed much greater resolution under certain circumstances, even down to sub-nm. One of the first of these methods to be developed was Förster resonance energy transfer (FRET). In FRET, two dye molecules are chosen such that the emission spectrum of one overlaps the absorption spectrum of the other. This energy transfer is extremely distance dependent, so it is possible to tell with angstrom resolution how far apart the two dyes are. This can be used for instance to determine when two bilayers fuse and their components mix. Another high resolution microscopy technique is fluorescence interference contrast microscopy (FLIC). This method requires that the sample be mounted on a precisely micromachined reflective surface. By studying the destructive interference patterns formed it is possible to individually resolve the two leaflets of a supported bilayer and determine the distribution of a fluorescent dye in each. Electrical Electrical measurements are the most straightforward way to characterize one of the more important functions of a bilayer, namely its ability to segregate and prevent the flow of ions in solution. Accordingly, electrical characterization was one of the first tools used to study the properties of model systems such as black membranes. It was already known