This is a prospective, longitudinal multicenter observational study comparing home to office spirometry and home to office weight and height measurements. The aim of the study is to estimate the accuracy and variability of home spirometric measurements over time, and to assess the feasibility and acceptability of home measurements.

After successful completion of the run-in period, participants will have 3 in-person visits, at which office spirometry will be performed and weight and height measured. Participants will perform home spirometry weekly during the study period. They will also electronically complete a weekly electronic patient reported outcome (ePRO) Within one week of each in-person visit, they will measure height and weight at home and perform home spirometry with virtual coaching by site research staff. They will complete a brief ePRO every 4 weeks regarding acceptability and feasibility of home spirometry in research. Within two weeks after study completion, a purposive subsample will complete an exit interview.

Inclusion Criteria:

• Documentation of a CF diagnosis
• Clinically stable
• ≥6 years of age at Screening Visit
• During the run-in period, performed acceptable home spirometry at least twice without virtually coaching and once with virtually coaching

Exclusion Criteria:

• History of lung transplantation
• Initiation of a highly effective modulator therapy within 2 months before Screening Visit

Study participants will be recruited at Cystic Fibrosis Foundation's Therapeutics Development Network study sites