A multicenter randomized, double-blind, parallel group, placebo-controlled, exploratory phase IIa study in subjects with Idiopathic Pulmonary Fibrosis (IPF) to evaluate safety, tolerability, PK and PD of GLPG1690. Male and female subjects aged 40 years or older will be screened to determine eligibility. The screening period will be up to 4 weeks. At baseline, eligible subjects will be randomized in a 3:1 ratio to GLPG1690 or matching placebo administered for 12 weeks. The subjects will visit the study center at screening, baseline, week 1, 2, 4, 8 and 12 and for a follow up visit 2 weeks after the last administration of study drug. Planned assessments: Adverse event reporting, clinical laboratory tests, vital signs, physical examination, 12-Lead-ECG, PK blood sampling, biomarker blood/BALF samples, Spirometry, St George's respiratory questionnaire, high-resolution computed tomography (HRCT).