<p> &ldquo;Mental Labor&rdquo; has been identified as an important, taxing, yet often invisible, aspect of family work that is disproportionately performed by mothers compared to fathers (DeVault, 1991; Lee &amp; Waite, 2005; Mederer, 1993; Offer, 2014; Thorstad, 2003; Walzer, 1996; Winkler &amp; Ireland, 2009). While researchers agree that mental labor (ML) needs to be included in family work measures, there has been no unified application of terminology, nor has any study been conducted for the express purpose of understanding ML phenomena. To provide a more comprehensive understanding of this construct, a phenomenological focus group study was designed to elicit rich descriptions of the thinking work performed by mothers of young children. Twenty-five women parenting children under age 12 in two-parent homes were recruited from community-based groups. Seven focus groups were conducted and verbatim transcripts were submitted for Interpretive Phenomenological Analysis (IPA) following Smith and Osborn&rsquo;s (2003) guidelines and Palmer, Larkin, de Visser, and Fadden&rsquo;s (2010) recommendations for IPA with focus groups. Quality assurance included independent coding, peer review, member check, follow-up questionnaires, analysis of group-process, and self-reflection. ML emerged as a diverse set of mental activities and preoccupations unified by their function in family life. The following definition is proposed: ML is thinking performed for the purpose of accomplishing family goals. Effective mental laboring is the means by which parents leverage resources and coordinate family operations to ensure productivity and well-being. A thematic hierarchy describing the nature, content, impact, and context of ML is presented. In the content domain, six forms of ML were identified: (a) planning and strategizing, (b) monitoring and anticipating needs, (c) metaparenting (i.e., meta-reflection involved in developing and applying a parenting philosophy), (d) knowing (e.g., information processing, learning, remembering), (e) managerial thinking (e.g., coordination, delegation, instruction, evaluation), and (f) self-regulating. Effective mental labor can be empowering. However, the themes &ldquo;mothers as mental laborers&rdquo; and &ldquo;mental labor invisibility&rdquo; confirm that unrecognized mental labor is problematic. Invisible mental work can isolate a mental laborer and distort her sense of self. These and other findings are described, followed by a discussion of clinical implications and directions for future research.</p>