Photoplethysmography (PPG) is a non-invasive technique that measures blood flow using infrared light. It is widely used for monitoring heart rate, blood oxygen saturation, and blood pressure. However, its diagnostic potential for assessing various cardiovascular conditions, such as atherosclerosis and vascular disease, remains underexplored. This paper reviews PPG signal processing challenges, features, and applications. PPG signals are affected by various artifacts, including powerline interference, motion artifacts, low amplitude signals, and premature ventricular contractions. These artifacts can distort the signal and affect the accuracy of diagnostic features. To improve signal interpretation, first and second derivatives of the PPG waveform are used to identify critical points and enhance feature extraction. The first derivative helps in identifying diastolic points and peak-to-peak time, while the second derivative provides information on vascular stiffness and aging. Key features derived from PPG signals include systolic amplitude, pulse width, pulse area, peak-to-peak interval, pulse interval, augmentation index, and large artery stiffness index. These features are used to assess cardiovascular health, detect arrhythmias, and monitor conditions such as hypertension and atherosclerosis. The second derivative of PPG, known as acceleration plethysmography (APG), provides additional insights into vascular aging and disease. APG features, such as the b/a, c/a, d/a, and e/a ratios, are used to evaluate arterial stiffness and vascular health. The paper also discusses the application of PPG in various clinical settings, including cardiovascular monitoring, stress assessment, and disease diagnosis. Despite its potential, the diagnostic value of PPG features is still not fully understood, and further research is needed to enhance its clinical utility. PPG is a promising technology due to its simplicity, low cost, and non-invasive nature, making it suitable for widespread use in healthcare.Photoplethysmography (PPG) is a non-invasive technique that measures blood flow using infrared light. It is widely used for monitoring heart rate, blood oxygen saturation, and blood pressure. However, its diagnostic potential for assessing various cardiovascular conditions, such as atherosclerosis and vascular disease, remains underexplored. This paper reviews PPG signal processing challenges, features, and applications. PPG signals are affected by various artifacts, including powerline interference, motion artifacts, low amplitude signals, and premature ventricular contractions. These artifacts can distort the signal and affect the accuracy of diagnostic features. To improve signal interpretation, first and second derivatives of the PPG waveform are used to identify critical points and enhance feature extraction. The first derivative helps in identifying diastolic points and peak-to-peak time, while the second derivative provides information on vascular stiffness and aging. Key features derived from PPG signals include systolic amplitude, pulse width, pulse area, peak-to-peak interval, pulse interval, augmentation index, and large artery stiffness index. These features are used to assess cardiovascular health, detect arrhythmias, and monitor conditions such as hypertension and atherosclerosis. The second derivative of PPG, known as acceleration plethysmography (APG), provides additional insights into vascular aging and disease. APG features, such as the b/a, c/a, d/a, and e/a ratios, are used to evaluate arterial stiffness and vascular health. The paper also discusses the application of PPG in various clinical settings, including cardiovascular monitoring, stress assessment, and disease diagnosis. Despite its potential, the diagnostic value of PPG features is still not fully understood, and further research is needed to enhance its clinical utility. PPG is a promising technology due to its simplicity, low cost, and non-invasive nature, making it suitable for widespread use in healthcare.