WHAT MAKES OBJECTS SO STICKY? Removing one's finger from a sticky surface often requires an unexpectedly large amount of work, sometimes up to 10,000 times more than simple theoretical considerations would suggest. The forces primarily involved in making objects sticky are the weak attractions between molecules known as van der Waals forces, but their effect is enhanced by mechanisms whose exact nature and role have remained a mystery. Moreover, in controlled experiments where a metallic probe is removed from a sticky polymer at a constant rate, no one has explained the observed sequence of forces, which quickly reach a peak value, then remain roughly constant before dropping to zero. Now, researchers in France (Cyprien Gay and Ludwik Leibler, CRNS-Elf Atochem, cgay@pobox.com, 011-33-147-59-1494) suggest that a combination of surface roughness and air suction effects is what makes things sticky. In their theory, air bubbles are trapped as the rough, wavy surfaces of the metallic probe and of the deformable polymer touch each other. Pulling apart the surfaces causes the bubbles to change shape. At first this creates a suction-cup effect which makes it harder to separate the surfaces (corresponding to the force peak), until air rushes in. Then, isolated bubbles connect and evolve into a network of contact points between the probe and polymer. Fractures that propagate through this network reduce the force required to separate the surfaces, and keep it at a plateau before the probe is finally removed, dropping the force to zero. Developing a more sophisticated understanding of stickiness will help researchers better design adhesives, coatings and paints. (Gay and Leibler, Physical Review Letters, 1 February 1999.)