This thesis examines the structuring role of timbre through the pianistic repertory of the first half of the nineteenth century, an exploratory period in which timbre, as multidimensional compound, occupies a central place. Based on an architectonic and organic conception of form, it conveys acoustics and psychology, in a transdisciplinary perspective. Relationship between timbre and language is based on the timbral resources of writing. This material, provided with strong structural potentialities, is modelled by pianistic and textural factors in interaction. Low-level timbral units, delimited by different types of articulations, find their cohesion in timbral groupings provided with emerging properties. The resulting orientated structures converge or diverge with the other musical dimensions. Formal deployment of timbre involves timbral associations, giving rise to orientated and polarized spaces and to network structures. Timbral prolongations, implying temporal extension, generativity and recursion of form, concern the spectral and temporal dimensions of timbre and question the notion of fundamental structure. Timbral hierarchies, considered in terms of subordination and reduction, involve fractal and treelike structures. Relationship between timbre and overall formal plan implies the examination of high-level timbral units, resulting from statistical and syntactic groupings, and whose articulations present many similarities with low level. The typology of forms renders the resulting structures’ diversity and brings to light the notions of climax, symmetry, progression, anticipation and return. Timbre, structured in interrelated levels, thus constitutes a dimension essential to the comprehension of nature and evolution of pianistic forms.