During the early years in our career as data scientists, we were bewildered by all kinds of data science hype. There was a lack of definition of many basic terminologies such as “Big Data” and “Data Science.” How many GBs of data were big data? What was data science? What was the difference between the sexy title “Data Scientist” and the traditional “Data Analyst?” How suddenly came all kinds of machine learning and deep learning algorithms? All those struck us as confusing and vague as real-world data scientists! However, we always felt something real in data science applications, and it develops very fast. After applying data science for many years, we now have a much better idea about data science in general. This book is our endeavor to make data science a more concrete and legitimate field. In addition to “hard” technical aspects, the book also covers soft skills and career development in data science.