A technique for the manipulation of Langmuir-monolayers at the air/water interface is presented. Optical tweezers are combined with fluorescence and Brewster angle microscopy to produce a system capable of mechanical and thermal handling of monolayers on a micrometer scale. The viscoelastic, electrical, and thermodynamic properties of the monolayer can be determined by analysis of the perturbations of its structure. A method for force and heat calibration of the tweezers is given. Both kinds of micromanipulations are applied to the star shaped condensed domains in liquid expanded surroundings of bis[8-(1,2-dipalmitoyl-snglycero-3 -phosphoryl)-3,6-dioxaoctyl]disulfide ("thiolipid") monolayers. The stability of the stars and the consequence of their interlocking on the interfacial flow are investigated.