This work examines the adhesion dynamics between copolymer vesicles of poly(dimethylsiloxane)-poly(ethylene oxide)[PDMS-PEO], where one membrane spreads over the second to partially engulf it. The project considers limiting extremes with respect to the translational diffusion of ligands and receptors in the membrane: In one extreme, dense membrane functionalization facilitates adhesion without requiring translational diffusion of receptors while in the other extreme, translation diffusion of ligands and receptors within the plane of the membrane surely dominates kinetics. The PDMS-PEO was functionalized with biotin to enable ligand-receptor binding to avidin-functionalized membranes. Using micropipettes, an avidin-coated vesicle was brought into contact with biotinylated one and the contact area and angle monitored in time. Densely functionalized vesicles, where diffusion was unimportant, showed strong and irreversible adhesion dynamics which could be described in three steps: pre-adhesive latency period, rapid adhesion which was initiated suddenly, and finally gradual relaxation. With 50 or more mol% functionalization, all three phases proceeded relatively quickly and independent of membrane functionality. At lower functionalities, the process was slower, as a result of diffusion, and roughly in proportion to the density of ligands and receptors. At the lowest functional densities, adhesion proceeded without membrane deformation, giving the appearance of a latency period, but still with irreversible adhesion. The maximum adhesion contact angles were almost same regardless of the initial membrane tensions, their functional density, or the tension ratio between substrate and adherent one. This suggests the ultimate state is dominated by the irreversibly binding ligands and receptors, though membrane mechanics affects adhesion dynamics.