Rollover Subjects Inclusion Criteria:  Pediatric subjects with ACH who have completed study activities in a previous QED-sponsored interventional study with infigratinib. Subjects and parent(s) or legally authorized representatives (LARs) are willing and able to comply with study visits and study procedures. Subjects are able to swallow oral medication. If sexually active, subject must be willing to use a highly effective method of contraception while taking study drug and for 1 month after the last dose of study drug. The PI, or a person designated by the PI, will obtain written informed consent from each subject's LAR and the subject's assent, when applicable, before any study-specific activity is performed.  Rollover Subjects Exclusion Criteria:  Subject has concurrent circumstance, disease, or condition that, in the view of the PI and/or sponsor, would interfere with study participation or safety evaluations. Subjects who developed a medical condition that will require the initiation of treatment with a prohibited medication. Subjects that have reached final height or near final height.  Key Inclusion Criteria for Treatment Naïve Subjects  Subject must be 3 to <18 years of age (inclusive) at screening and have growth potential. Subjects who have a diagnosis of ACH, documented clinically and confirmed by genetic testing. Subjects have at least a 6-month period of growth assessment in the PROPEL study (Protocol QBGJ398 001) before study entry. In girls ≥10 years of age or girls of any age who have experienced menarche, having a negative pregnancy test. If sexually active, subject must be willing to use a highly effective method of contraception while taking study drug and for 1 month after the last dose of study drug. The PI, or a person designated by the PI, will obtain written informed consent from each subject's LAR and the subject's assent, when applicable, before any study-specific activity is performed.  Exclusion Criteria for Treatment Naïve Subjects  Subjects who have hypochondroplasia or short stature condition other than ACH (e.g., trisomy 21, pseudoachondroplasia, psychosocial short stature). Subjects who have significant concurrent disease or condition that, in the view of the PI and/or sponsor, would represent an increased risk to the subject or would interfere with study participation or safety evaluations. Subjects who have a history of malignancy. Subjects who are currently receiving treatment with agents that are known strong inducers or inhibitors of cytochrome P450 (CYP) 3A4. Subjects who have received treatment with growth hormone, insulin-like growth factor 1 (IGF 1), anabolic steroids or any investigational or approved drug for the treatment of ACH in the previous 6 months.