This paper re-examines the universally held assumption that the gospel of Luke and the Acts of the Apostles were written-edited by a unitary author, traditionally known as “Luke.” Reassessment of the internal and external evidence for single authorship reveals a shakier foundation than previously thought and, hence, calls for further scrutiny. A newly designed analysis of Luke and Acts suggests the existence of highly significant differences in prose style. In particular, selected from each book is a set of key passages that comprises the least contested authorial stratum, namely, seams and summaries. Functioning as literary sutures, seams and summaries unite texts or complexes of text and thereby provide prime “soil” for analysis. Since these texts were composed in the first century (or probably second century, in the case of Acts), it is fitting to examine them for the presence of prose compositional conventions in use at that time, for example, hiatus, dissonance, prose rhythm, and structural elements. Results of this fresh analysis show that prose compositional patterns in Luke and Acts deviate sharply and actually distinguish the two books’ authorship beyond a reasonable doubt. Although generally undisputed, the authorial unity of Luke and Acts must be called into question and the far-reaching implications of such a claim fully investigated.