The phase formation of 2,2＇-bipyridine (2,2＇-BP) on Au(111) in 0.05 M KClO4 has been studied using capacitance measurements, cyclic voltammetry and in situ scanning tunneling microscopy (STM). Two ordered organic adlayers were found and imaged in situ with molecular resolution. Between -0.10 and 0.30 V 2,2＇-BP forms an ordered pattern IIa of asymmetric, individual ＇angular＇ segments. The average repeat distance is estimated to be d = 3.5 +/- 0.3 nm. The structure is composed of ＇long＇ and ＇short＇ slacks, their lengths vary between three and twenty molecules The enclosed angle, delta = 65 +/- 3 degrees, is slightly larger then 60 degrees, the symmetry element imposed by the hexagonal substrate surface geometry. At potentials more positive then 0.40 V a second ordered monolayer, labeled phase I, is formed. This structure is characterized by parallel molecular chains. The distances between adjacent stacking rows and adjacent molecules are b = 10.1 +/- 0.5 and a＇ = 3.3 +/-0.2 Angstrom. A commensurate 4 x 2 root 3 unit cell is proposed. The potential-induced structural change from IIa to I proceeds according to a two-dimensional order-disorder-order phase transition. This mechanism as well as the accompanied structural changes of the electrode surface were studied in detail by in situ STM.