The study of timbre and orchestration in music research is underdeveloped, with few theories to explain instrumental combinations and orchestral shaping. This chapter will outline connections between the orchestration practices of the nineteenth and early twentieth centuries and perceptual principles based on recent research in auditory scene analysis and timbre perception. Analyses of orchestration treatises and musical scores reveal an implicit understanding of auditory grouping principles by which many orchestral effects and techniques function. We will explore how concurrent grouping cues result in blended combinations of instruments, how sequential grouping into segregated melodies or stratified (foreground and background) layers is influenced by timbral similarities and dissimilarities, and how segmental grouping cues create formal boundaries and expressive gestural shaping through changes in instrumental textures. This exploration will be framed within an examination of historical and contemporary discussion of orchestral effects and techniques.