Increasingly, a female body that is both lean and toned (i.e., a fit or athletic female body) is being endorsed by women and media as desirable (Bozsik, Whisenhunt, Hudson, Bennett, & Lundgren, 2018; Tiggemann & Zaccardo, 2016). Preliminary research suggests that media are promoting this body standard as being an outcome of disciplined behavioural practices (Jong & Drummond, 2016), and that women associate this body type with health, confidence, social acceptance and dedication (Raggatt et al., 2018). Ironically however, research has found that women who are exposed to (Prichard, McLachlan, Lavis, & Tiggemann, 2017), or propagate (Holland & Tiggemann, 2017), fit ideal content on social media, are at risk of experiencing disordered body image, eating and exercise outcomes. From a sociocultural perspective, these findings imply that women perceive a fit body as ideal, and that internalisation of fit ideal desirability may be harmful to women’s health (Ata, Schaefer, & Thompson, 2015; Tiggemann, 2011). However, research explicitly investigating whether or not internalisation of the fit ideal is harmful to women’s health, has not yet been undertaken, primarily because a measure of fit ideal internalisation currently does not exist within the literature. Before such a measure can be developed, the cognitions and attitudes that underlie the perception that a fit body type is ideal must be better understood, and the factors that differentiate women who prefer a fit body standard relative to existing body standards such as thinness require investigation. This research program was designed to address these gaps in the literature. The first of the three empirical papers reports on a study conducted with 356 female participants, aged 17–30 years (M = 20.57, SD = 3.25) that assessed whether, given the anecdotal perception of the fit (lean and toned) female body standard as healthier than thinness, simultaneous internalisation of a muscular ideal would mitigate the negative health outcomes (i.e., negative affect, body dissatisfaction, bulimic symptoms, and dieting ) of women who internalised a thin ideal. It was also of interest to ascertain whether, in women who internalised the muscular ideal, compulsive exercise and supplement use would be amplified by those who simultaneously endorsed the thin ideal. The results did not support the assertion that internalisation of a fit body ideal is healthier for women, as no significant moderation effects of muscular internalisation were found for women who internalised thinness (and visa-versa). The second of the three empirical papers outlines a study that investigated the socio-cultural meaning of a fit female body relative to one of thinness only. The study assessed 547 female participants aged 16-65 years (M = 24.0, SD = 8.5) and investigated differences (attitudinal, socio-demographic, and behavioural) between women who personally endorse a thin versus a fit body shape as ideal. Using computer generated 3D images as stimuli, women rated their preferences and beliefs about four main body shapes (overweight, hyper-muscular, thin and fit). Most women reported preferring a body characterised by leanness and muscle tone, yet believed that the wider society preferred a female body characterised by thinness only. Women who personally preferred a fit (rather than a thin) body reported less peer pressure to be thin, were older, and engaged in more exercise. Most women (regardless of body preference) believed that fit and hyper-muscular body types (relative to overweight and thin bodies) were higher in discipline, life control, self-confidence, mental health and physical health. Thin and fit bodies were more likely to be rated positively in terms of popularity and sexual desirability. Differentiating women who preferred a fit over a thin body, was that women who preferred a fit body ideal held more negative beliefs about the thin body type (relative to a fit, muscular, and sometimes an overweight body). Overall, the findings imply that most women associate muscularity (more than thinness) with character strength and health yet see thinness as a necessary ingredient for social approval. The fit ideal appears to embody both these intrinsic and extrinsic characteristics. The third of the three empirical papers draws on information gleaned from the first two papers, to develop and validate a psychometrically sound measure for assessing fit ideal internalisation; the Fit Ideal Internalisation Test (FIIT). Fit ideal internalisation was operationalised multidimensionally through three factors; fit idealisation (i.e., concern/preoccupation with fit ideal congruence), fit overvaluation (i.e., linking attainment of the fit ideal to personal value and social belonging) and fit behavioural drive (engagement in behaviour to achieve the fit ideal). Three separate samples of women were used to 1) establish the three factor structure of the scale (N = 300, age 16-51), 2) confirm the three factor structure of the scale and conduct validity testing (N = 354, age 16-63) and 3) to examine the two-week test-retest reliability of the scores (N = 67, age 17-50). Findings supported the convergent, discriminant and incremental validity of the FIIT subscale scores (and total score). Items loading highly on each of the factors had good inter-item correlations, and the two-week test-retest reliability was high. Scores on the FIIT were associated with negative health consequences for women, particularly body dissatisfaction and compulsive exercise. Overall, the results supported the three-factor structure of the FIIT, and the utility of a total score, and suggest that fit ideal internalisation is associated with body image, eating and exercise maladjustment. In summary, the results of this research compendium confirm the supposition that the fit ideal holds unique appeal to women, beyond that of thinness or muscularity in isolation, and suggest that despite social perception, desiring, valuing and striving for a fit looking body, is likely to be associated with ill-health.