David Busby has been a Linux system's admin for around 12 years now and almost always being in a varied role over the years be it development, network admin, support, DBA changing onto a day-to-day basis.

Whenever time permits, he contributes to the EPEL packages for OpenStack and generally follows OpenStack's progress as much as possible.

He has an interest in Infosec, and as a result is generally paranoid about security. He is also familiar with Metasploit, sqlmap, john, and oclHashCat, and has also written a few python tools, and experimented in Golang.

He holds a 2nd Dan black belt in Ju-Jitsu and assists with teaching at a local non-profit club. He also helps to teach a computing class for children at a local school, using Raspberry Pi.

Stamati Crook is a professional programmer with his own software house and consultancy on the south coast of England. He has been involved in teaching Scratch to children at local primary schools and also hopes that his own three children will begin to show more interest in creating games rather than just playing them. His wife, Kathy, also uses Scratch daily in her classroom and you can find lesson plans and resources for children, parents, and teachers learning and teaching Scratch at http://www.redware.com/scratch.

Andrew Johns has been a web developer since 1999. He became a STEM Ambassador and Code Club volunteer in 2012, teaching Scratch to primary school children. He currently works for London-based design agency, Pretty, as a Technical Lead. This is the first book for which he has acted as a Technical Reviewer.

Martina Kabátová is a teacher and a researcher in the field of Computer Science education. After completing her PHD, she began to work as an Assistant Professor at Comenius University in Bratislava, Faculty of Mathematics, Physics and Informatics, Department of Informatics Education. Among her responsibilities are several university lectures on programming, educational robotics, and research methodology. Currently, she focuses on educational programming (especial for very young children). She is an author of several study materials and many conference papers dealing with various aspects of Computer Science education. In 2013, she co-authored a book Transforming Schools in Digital Age, with Prof. Ivan Kalaš, which summarizes the role of digital technology in education. Martina Kabátová also illustrated this book and she is the author of many illustrations for other computer science textbooks, educational software, and MicroWorlds, and for the Slovak Bebras contest for children in informatics.

Pedro Neves Rito has been working as a professional trainer in the area of information technology and communications for more than 16 years, and as a teacher in higher education for the last six years. He has a Master's degree in Multimedia in Education and is currently a student of the Doctoral program in information systems and technologies. He has used Scratch as a tool for an introduction to programming. Lately, he's been exploring physical computing and Scratch, particularly the use of the Arduino, with the perspective of building activities for primary students. This work has been developed with the help of teachers of different levels of education.

He is currently also an assistant professor at Polytechnic Institute of Viseu, at the School of Education, working in the Department of Communication and Art, in the area of Information Technology and Communication. He works with higher education students, particularly in plastic arts and multimedia, and those pursuing primary education courses (future teachers) and also some that are pursuing Master's courses. In addition to being a teacher in these areas, he has supported a few initiatives outside school that are related to the use of Scratch.

He has started some individual projects, including the writing of two books, which is ongoing. In recent years, he has dedicated most of his time to contributions, by publishing and presenting scientific articles at conferences and some other documents to print media.

Forrest Y. Yu is an author of two books on operating systems. He has a wide range of interests and experiences, including desktop applications, web services, LBS, operating systems, cloud computing, and so on. Recently, he has been working with Amazon building the next generation information security platform and tools. He has a blog http://forrestyu.com/ where you can find more information about him.