Introduction Controversies surrounding Patient-Reported Outcome Measures (PROMs) and the cumbersome-nature of movement analysis-based (MAB) methods for shoulder function evaluation make the exploration of alternatives needed. Research aimed at the simplification of MAB outcome measures had demonstrated previously that the B-B Score, which relies on two movements only, was valid for out-of-laboratory evaluations of shoulder function. Nevertheless, further investigations were needed to optimise testing procedures, test the B-B Score’s capability of acquisition using a user-friendly device, and critically evaluate its measurement properties in comparison to current methods. Objective The aim of this thesis was to develop and assess the simplest possible MAB shoulder function scoring procedure for clinical measurement. Methods The research included four steps: 1) Optimisation of the B-B Score testing procedure (Phase 1 study [data-driven]), 2) Comparison of measurements using a smartphone or an inertial sensor system (Phase 2 study [data-driven]), 3) Validation in frequentlyoccurring pathologies (rotator cuff conditions, instability, fracture, capsulitis) (Phase 3 study [data-driven]), 4) Benchmarking of the new approach with concurrent MAB outcome measures and PROMs (literature review). Results Amongst the tested methods, the B-B score was optimised by using the mean of three replicates in the computation of the range of accelerations by angular velocities. The comparison of easily-used smartphone and reference device showed non-significant differences and excellent relationships between measurements (Intraclass Correlation Coefficient [ICC=0.97]). The smartphone’s B-B Score intra-rater and inter-rater reliability was excellent (ICC=0.92), but limits of agreement could reach up to ±19.4%. The score was responsive (area under the curve [AUC≥0.70]) and demonstrated excellent discriminative power between patients and controls (AUC≥0.90), except for shoulder instability (AUC=0.67). The correlations with PROMs were moderate to high. The benchmarking established that the measurement properties of the B-B Score compared equivalently with those of PROMs and MAB outcome measures, except for shoulder instability. Conclusion Shoulder function can be efficiently evaluated using a simple scoring procedure performed with a smartphone, which facilitates its objective assessment. Further research is needed to understand how best to reduce the effects of variability associated with single measurements in order to optimise clinical applicability and to explore the B-B Score’s properties in other situations requiring functional assessments of the shoulder. . Keywords: shoulder, shoulder function; outcome assessment; validation studies, reliability and validity; inertial sensors; smartphone sensors; body-worn sensors; kinematics; sensitivity and specificity.