The Clinical Practice Research Datalink (CPRD) is a large primary care database containing anonymized medical records from general practitioners (GPs) in the UK, covering over 11.3 million patients from 674 practices. It includes data on demographics, symptoms, tests, diagnoses, therapies, health-related behaviors, and referrals to secondary care. Over half of the patients are linked to additional datasets, including hospital data, cancer registration data, and mortality records. The CPRD is widely used internationally for epidemiological research and has been used in over 1000 studies published in peer-reviewed journals. However, researchers must be aware of the complexity of routinely collected electronic health records, including variable completeness, misclassification, and the need to develop disease definitions for research. The CPRD data are derived from routine clinical practice and are used for epidemiological studies, requiring extensive data processing and an understanding of how data are recorded and stored. The data are collected daily by practices and uploaded monthly to the CPRD secure servers. The CPRD has broad ethics approval for observational research and may require separate ethical approval for other uses involving patient involvement. The CPRD is jointly funded by the Medicines and Healthcare Regulatory Agency (MHRA) and the National Institute for Health Research (NIHR), and it operates within UK and European laws to protect patient confidentiality. The CPRD covers a broad range of health-related research topics, including pharmacoepidemiology, comparative effectiveness research, health services research, and randomized controlled trials. It has been used to show no association between MMR vaccine and autism, and an association between oral corticosteroid use and increased fracture risk. The CPRD data are representative of the UK population in terms of age, sex, and ethnicity, but may not be representative of all practices in the UK based on geography and size. Data quality is influenced by the Quality and Outcomes Framework, which encourages the recording of key data items. However, data quality can vary due to the nature of data entry by GPs during routine consultations. The CPRD provides data dictionaries and coding dictionaries to researchers, and guidance on creating code lists is available. Researchers must undertake comprehensive data quality checks before undertaking a study. The CPRD has two sets of data quality criteria: acceptability for patients and up to standard (UTS) time for practices. These criteria do not ensure data quality, but the CPRD recommends that these measures are used as a first step to selecting research-quality patients and periods of quality data recording. The CPRD is a valuable resource for health research, but researchers must be aware of the potential for missing data, misclassification, and the need for careful data management.The Clinical Practice Research Datalink (CPRD) is a large primary care database containing anonymized medical records from general practitioners (GPs) in the UK, covering over 11.3 million patients from 674 practices. It includes data on demographics, symptoms, tests, diagnoses, therapies, health-related behaviors, and referrals to secondary care. Over half of the patients are linked to additional datasets, including hospital data, cancer registration data, and mortality records. The CPRD is widely used internationally for epidemiological research and has been used in over 1000 studies published in peer-reviewed journals. However, researchers must be aware of the complexity of routinely collected electronic health records, including variable completeness, misclassification, and the need to develop disease definitions for research. The CPRD data are derived from routine clinical practice and are used for epidemiological studies, requiring extensive data processing and an understanding of how data are recorded and stored. The data are collected daily by practices and uploaded monthly to the CPRD secure servers. The CPRD has broad ethics approval for observational research and may require separate ethical approval for other uses involving patient involvement. The CPRD is jointly funded by the Medicines and Healthcare Regulatory Agency (MHRA) and the National Institute for Health Research (NIHR), and it operates within UK and European laws to protect patient confidentiality. The CPRD covers a broad range of health-related research topics, including pharmacoepidemiology, comparative effectiveness research, health services research, and randomized controlled trials. It has been used to show no association between MMR vaccine and autism, and an association between oral corticosteroid use and increased fracture risk. The CPRD data are representative of the UK population in terms of age, sex, and ethnicity, but may not be representative of all practices in the UK based on geography and size. Data quality is influenced by the Quality and Outcomes Framework, which encourages the recording of key data items. However, data quality can vary due to the nature of data entry by GPs during routine consultations. The CPRD provides data dictionaries and coding dictionaries to researchers, and guidance on creating code lists is available. Researchers must undertake comprehensive data quality checks before undertaking a study. The CPRD has two sets of data quality criteria: acceptability for patients and up to standard (UTS) time for practices. These criteria do not ensure data quality, but the CPRD recommends that these measures are used as a first step to selecting research-quality patients and periods of quality data recording. The CPRD is a valuable resource for health research, but researchers must be aware of the potential for missing data, misclassification, and the need for careful data management.