In this thesis, I have attempted to analyze conscience as an ethical phenomenon in Shakespeare’s Richard III and Macbeth. The two plays have often been compared due to many similarities in terms of plot, characters and genre, and therefore I thought it would be interesting to look at the differences between the plays in their manner of representing conscience. The discussion consists of three parts: the first chapter examines the lexical meanings of different occurrences of the word ‘conscience’ in several Shakespeare plays, and by examples demonstrates the multiplicity of meanings which might otherwise be unknown to general readers. The second chapter traces some of the historical developments in the early modern theatre and in techniques of characterization, and provides background information for understanding the character of Richard III and other Shakespearean villains. The third chapter attempts to describe conscience as a phenomenon in Richard III and Macbeth. The analysis demonstrates how conscience manifests itself as a physical and external phenomenon in Richard III, and how conscience appears as an incorporeal and internal phenomenon in Macbeth. The very nature of theatrical representation at the time these plays were written may have affected how conscience is represented in the respective plays. Richard III is a relatively early play (ca. 1592), and is influenced by and alludes to earlier allegorical plays. This may have influenced the representation of conscience as an external element which affects the characters from the outside. Macbeth is a later play (ca. 1606), and generally there is a greater depth in characterization and insight into the characters’ thoughts and emotions in this period. This internal emphasis may have facilitated the representation of conscience as an internal faculty of the soul.