Objective. Outcome Measures in Rheumatology (OMERACT) Filter 2.1 revised the process used for core outcome measurement set selection to add rigor and transparency in decision making. This paper describes OMERACT’s methodology for instrument selection. Methods. We presented instrument selection processes, tools, and reporting templates at OMERACT 2018, introducing the concept of “3 pillars, 4 questions, 7 measurement properties, 1 answer.” Truth, discrimination, and feasibility are the 3 original OMERACT pillars. Based on these, we developed 4 signaling questions. We introduced the Summary of Measurement Properties table that summarizes the 7 measurement properties: truth (domain match, construct validity), discrimination [test-retest reliability, longitudinal construct validity (responsiveness), clinical trial discrimination, thresholds of meaning], and feasibility. These properties address a set of standards which, when met, answer the one question: Is there enough evidence to support the use of this instrument in clinical research of the benefits and harms of treatments in the population and study setting described? The OMERACT Filter 2.1 was piloted on 2 instruments by the Psoriatic Arthritis Working Group. Results. The methodology was reviewed in a full plenary session and facilitated breakout groups. Tools to facilitate retention of the process (i.e., “The OMERACT Way”) were provided. The 2 instruments were presented, and the recommendation of the working group was endorsed in the first OMERACT Filter 2.1 Instrument Selection votes. Conclusion. Instrument selection using OMERACT Filter 2.1 is feasible and is now being implemented.