Physiotherapist visual assessment of lower extremity dynamic alignment during functional screening tests is common when assessing clients for risk of injury and during rehabilitation. However the reliability and validity of visual assessment for several functional tests has not been reported, and for other tests needs clarification. The aims of this thesis were to investigate: 1) reliability of kinematics during lower extremity functional screening tests and their association with function (running and landing); and 2) reliability and validity of visual assessment of dynamic alignment during functional tests. Three-dimensional (3D) and/or two-dimensional (2D) kinematics were measured in healthy adults and young athletes during small knee bend (SKB), lunge, hop lunge, step-down and drop jump functional tests. Within-day (ICC ≥0.85) and between-days (ICC ≥0.60) reliability was acceptable for the majority of kinematics. Associations between functional test kinematics and kinematics during running and landing were moderate to very large. Physiotherapists with a range of experience visually rated dynamic alignment during functional tests using segmental and overall body approaches and dichotomous and ordinal scales. Mean intra-rater agreement was moderate to good [Agreement Coefficient 1 (AC1): 0.39 to 0.80] and inter-rater agreement fair to good (AC1: 0.22 to 0.71). Clinical experience, the use of a dichotomous scale and rating the knee position relative to the foot all improved agreement. Agreement on an overall rating was similar to segmental ratings. In young athletes, sensitivity (≥80%) and specificity (≥50%) were acceptable for visual ratings of SKB (double and single leg) but not drop jumps when compared to expert consensus ratings (aided by video slow motion). Experience and slower test velocity improved rating accuracy when rating young athletes [Diagnostic Odds Ratio (DOR): 1.6 to 4.9 times better]. Expert consensus ratings differentiated young athletes with different 2D kinematics (very likely to almost certainly) and 3D hip kinematics (likely to very likely) but not 3D knee abduction. The association between 2D and 3D kinematics during SKB and drop jumps in young athletes ranged from small to very large. Kinematics during lower extremity functional screening tests show sufficient reliability and link to function. Physiotherapist visual rating of dynamic alignment during these tests provides reliable and valid information that should assist in the clinical decision making process.