"Preface In pharmaceutical/clinical development of a test drug or treatment, relevant clinical data are usually collected from subjects with the diseases under study in order to evaluate safety and efficacy of the test drug or treatment under investigation. To provide accurate and reliable assessment, well-controlled clinical trials under valid study design are necessarily conducted. Clinical trial process is a lengthy and costly process, which is necessary to ensure a fair and reliable assessment of the test treatment under investigation. Clinical trial process consists of protocol development, trial conduct, data collection, statistical analysis/interpretation, and reporting. In practice, controversial issues evitably occur regardless the compliance of good statistical practice (GSP) and good clinical practice (GCP). Controversial issues in clinical trials are referred to as debatable issues that are commonly encountered during the conduct of clinical trials. In practice, controversial issues could be raised from, but are not limited to, (1) compromises between theoretical and real/common practices, (2) miscommunication and/or misunderstanding in perception/interpretation among regulatory agencies, clinical scientists, and biostatisticians, and (3) disagreement, inconsistency, miscommunication/misunderstanding, and errors in clinical practice. "--