Inclusion Criteria:

Participants must meet all the following criteria to be eligible for inclusion in this study:

1. Pulmonary fibrosis (PF) participants in Japan. Note: This includes those clinically recognized as having idiopathic pulmonary fibrosis (IPF) or progressive pulmonary fibrosis (PPF).

2. Participants who are ≥18 years of age at the time of providing informed consent via the web-based system.

3. Participants receiving outpatient care for pulmonary fibrosis (PF) who have been introduced to this study by a referring physician.

4. Participants who have a history of taking, or are currently taking, pirfenidone, nintedanib, or nerandomilast.

5. Participants who have experienced at least one antifibrotic (AF) therapy-related adverse event (AE).

   • Discontinuation group only

1) Participants who have not received AF therapy for at least 1 month prior to enrollment.

2) Participants whose AF therapy was discontinued within 6 months prior to enrollment.

3) Participants whose reason for discontinuing AF therapy includes at least one AF therapy-related AE.

• Continuation group only

  1. Participants who feel or have felt burdened by the experienced AE.

  2. Participants who have continued AF therapy for a specific period (≥6 months) at the time of enrollment.

     Exclusion Criteria:

     Participants meeting any of the following criteria will be excluded from the study:

  1. Participants currently participating in any interventional clinical trials (regardless of the study drug, excluding observational studies).
  2. Participants who have undergone lung transplantation.

• Discontinuation group only 1) Participants who discontinued AF therapy solely for reasons other than AE (e.g., financial reasons, disease progression).