Self-injurious cognitions (SICs) are cognitions about deliberately injuring oneself (self-injurious behavior [SIB]). Existing measures of the content of SICs provide varying coverage, highlighting a lack of consensus regarding which cognitions characterize SIB. Additionally, a central, unresolved conceptual and measurement issue concerns whether to conceptualize suicide attempts (SA) and nonsuicidal self-injury (NSSI), 2 forms of SIB, as separate constructs. We developed the Suicide Attempt Beliefs Scale (SABS) and the Nonsuicidal Self-Injury Beliefs Scale (NSIBS) to clarify which SICs characterize SA and NSSI and what factor structure best explains SA and NSSI cognitions. A series of factor analyses across 6 samples (N 3,313) revealed that the SABS consists of 7 correlated factors and the NSIBS consists of 10 correlated factors. Both instruments contain factors that describe how SIB relates to oneself and others and demonstrate moderate to excellent test-retest reliability over 2-4 weeks and strong internal consistency; 95% of the correlations between SABS and NSIBS subscales were r.5. Both instruments demonstrated small to moderate-sized correlations with a range of clinical variables, measures of well-being, and purportedly similar, existing SIB constructs. Various analyses indicate that SA and NSSI SICs are similar but distinct phenomena, supporting the use of separate terminology and definitions of SA and NSSI, and pointing to the importance of separating SA and NSSI in research and clinical practice. We hope that the development of the SABS and NSIBS may unify the field somewhat in its understanding and measurement of the basic constituent elements of SICs.