Dreams have been widely shared, analyzed, and explored for centuries. Throughout cultures and contexts, some dreams seem to leave a lasting trace on waking life, whereas other dreams are forgotten as quickly as they appear. This thesis focuses its efforts on the former category, known as impactful dreams. Impactful dreams are rare and distinguished by their effect on the dreamer’s thoughts, feelings, and/or behavior. Some dreams, including impactful dreams, also contain threatening oneiric material, which may be seen as mirroring threatening content the dreamer will have to face, or has already faced, in waking life. This thesis contributes to the study of dream content by using modern dream analysis methods to investigate impactful dreams and threats in dreams, drawing from a large normative sample of Canadians’ dreams, but also from the oneiric content found in works written by William Shakespeare. It was expected that both samples would share certain oneiric traits, but that Shakespeare’s in-play dreams would contain more oneiric threats, would have an impact on the dreamer by default, and would most notably affect the narrative of the play. In contrast, normative Canadian dreams were expected to show a lesser tendency towards both impact and threatening content. The first article explores all impactful dreams found within a normative sample of Canadian dreams, investigating their impactful dream type and their link to waking and dreaming mood. The second article does the same within the scope of Shakespeare’s fictional works, and compares the two samples in terms of dream impact, threats, and overall oneiric content.