This chapter explains the histogram which is a vertical bar chart that depicts the distribution of a set of data. A histogram makes it easy to see where the majority of values fall in a measurement scale. There is lot of information hidden in these histograms which are diagrammatically described with the background of normal histogram which allows understanding of variations in terms of shifting, size, notching etc. which directly correlates with the pathology of the sample. Author has elaborated the approach of interpretation of histogram and stress the importance of reading a histogram to come to a hidden diagnosis.