Per-oral endoscopic myotomy (POEM) has emerged as the endoscopic treatment of choice for achalasia, offering comparable symptom relief with laparoscopic Heller's cardiomyotomy. The main concern with POEM is the higher incidence of post-procedure gastroesophageal reflux disease (GERD), occurring in up to 50-60% of patients. In order to reduce the risk of GERD, endoscopic fundoplication has been developed as a novel procedure mimicking surgical anterior partial fundoplication that can be performed in the same session as POEM (POEM-F). Case series of POEM-F in patients with achalasia reported encouraging outcomes of low GERD rate of \ 12% at 1 year. Prospective comparative data between POEM-F and conventional POEM on post-procedure GERD is current lacking. The investigators therefore designed an international multicenter prospective randomized study to investigate the efficacy of POEM-F. The investigators postulate that POEM-F could reduce the incidence of post-procedure GERD when compared with conventional POEM. This is an international multicenter randomized controlled trial conducted between high volume expert centers from Hong Kong SAR, China, India and United States of America. Adult patients with manometry confirmed achalasia would be randomised to undergo POEM-F or POEM. The procedure would be performed by experts with vast experience in POEM. The primary outcome is the incidence of post-procedure GERD at 1 year, defined by the updated Lyon consensus. Secondary outcomes include technical and clinical success rates, adverse events, post-POEM endoscopic and manometry findings as well as patients' symptom scores. Sample size calculation Based on existing pilot comparative data on POEM-F and POEM, it is estimated that 84 patients would be required to demonstrate a difference in post-procedure GERD of 47.6% to 18.2%, with 80% power and false positive rate of 0.05, accounting for 10% loss to follow-up. Purpose and potential The current study proposal could demonstrate the superiority of POEM-F over POEM in reducing post-procedural GERD. It would also demonstrate the safety and reproducibility of the technique in expert centers across the globe. It could potentially replace conventional POEM as the preferred minimally invasive endoscopic treatment for achalasia.