This paper provides an overview of photoplethysmography (PPG) signals, focusing on their analysis and diagnostic applications. PPG is a non-invasive, low-cost, and convenient technique used to estimate skin blood flow using infrared light. The paper discusses the various types of artifacts that can affect PPG signals, such as powerline interference, motion artifacts, low amplitude, and arrhythmia. It also outlines the common structure of a PPG diagnostic system, which includes preprocessing, feature extraction, and diagnosis. The paper delves into the characteristics of PPG signals and their derivatives, including the first and second derivatives. The first derivative helps in defining the diastolic point and calculating the peak-to-peak time (ΔT) and crest time. The second derivative, also known as the acceleration plethysmogram (APG), provides more detailed information about blood flow and is used to calculate various indices such as the augmentation index and large artery stiffness index. The paper highlights the potential of PPG in early screening for atherosclerotic pathologies and regular GP-assessment. However, it notes that a full understanding of the diagnostic value of different PPG features is still lacking, and more research is needed. The review concludes by emphasizing the simplicity, low cost, and non-invasiveness of PPG, making it a promising technology for various health applications.This paper provides an overview of photoplethysmography (PPG) signals, focusing on their analysis and diagnostic applications. PPG is a non-invasive, low-cost, and convenient technique used to estimate skin blood flow using infrared light. The paper discusses the various types of artifacts that can affect PPG signals, such as powerline interference, motion artifacts, low amplitude, and arrhythmia. It also outlines the common structure of a PPG diagnostic system, which includes preprocessing, feature extraction, and diagnosis. The paper delves into the characteristics of PPG signals and their derivatives, including the first and second derivatives. The first derivative helps in defining the diastolic point and calculating the peak-to-peak time (ΔT) and crest time. The second derivative, also known as the acceleration plethysmogram (APG), provides more detailed information about blood flow and is used to calculate various indices such as the augmentation index and large artery stiffness index. The paper highlights the potential of PPG in early screening for atherosclerotic pathologies and regular GP-assessment. However, it notes that a full understanding of the diagnostic value of different PPG features is still lacking, and more research is needed. The review concludes by emphasizing the simplicity, low cost, and non-invasiveness of PPG, making it a promising technology for various health applications.