Writing is an important skill for language production. However, it is considered a difficult skill, particularly in English as a second language (ESL) contexts where students face many challenges in writing. Therefore, the present study was conducted with an aim to investigate problems in Pakistani undergraduate ESL learners' writing and factors that hinder their writing skills. It also aimed at obtaining suggestions on how to improve Pakistani ESL learners' writing skills. For this purpose, focus groups of Pakistani English language teachers'and undergraduate ESL learners were conducted. Writing samples were also collected from 30 ESL undergraduate learners to find the major problems in their writing. The interviews and essays were analyzed using thematic content analysis. The findings reveal that the major problems in Pakistani undergraduate ESL learners' writing are insufficient linguistic proficiency (including command over grammar, syntax and vocabulary), writing anxiety, lack of ideas, reliance on L1 and weak structure organization. These challenges are caused by various factors including untrained teachers, ineffective teaching methods and examination system, lack of reading and writing practice, large classrooms, low motivation and lack of ideas. The study also sheds light on the remedial measures such as increased reading, conscious and incidental vocabulary teaching, writing practice, trained teachers, reforms in the examination system, and writing competitions.