The authors report an investigation on the adsorption of pentacene molecules on Cu(110) in the submonolayer and monolayer ranges using scanning tunneling microscopy and low-energy electron diffraction. They identify and characterize three different phases for increasing pentacene coverage. For very low coverages [less than or similar to 0.1 ML (monolayer)] pentacene molecules are highly mobile and adsorbed uniaxially oriented along the [1 (1) over bar0] substrate direction. For higher coverages the ordering along the [001] direction improves, until a p(7 x 2) structure with imperfect registry along the [1 (1) over bar0] direction is formed at 0.89 ML. In both phases pentacene molecules occupy the Cu(110) troughs along the [1 (1) over bar0] direction. For even higher coverage (1.0 ML), a slight rotation of the molecular adsorption site gives rise to a complex ((61)(-14)) structure based in a c(12 x 2) cell. The appearance of two domains generates a long-range wavelike ordering. Annealing, of the adlayer results in the formation of supramolecular complexes. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3013855]