How to use experiments to drive faster, more informed decision making.

What are people saying about the book?

"Answering the question of 'What do you do after you get out of the b­uilding?' Testing with Humans is a 'must have' book for entrepreneurs."

Steve Blank, entrepreneur, educator and author of The Startup Owner's Manual

"Testing with Humans is the ideal follow-up to Constable and Rimalovski’s Talking to Humans. It literally takes what they've already taught us to the next level--from customer discovery to experimenting with those customers in order to find product-market fit. All the steps for designing, building, and launching experiments are here, along with a host of examples and great advice born of real experience."

Eric Ries, author of The Lean Startup and The Startup Way

"A brilliant blend of principles, examples, templates and checklists on a topic that is so essential to entrepreneurs. This book makes you want to get out of the building and run experiments even if you are not working on a startup!"

Singari Seshadri, head of the Stanford University Venture Studio

"Testing With Humans explains the scientific method to explore the biggest unknowns in your business. It provides the essential tools to critically test your hypothesis on the most difficult test subject known to man, namely man."

Errol Arkilic, founding Program Director, NSF I-Corps & CEO, M34 Capital

"Giff and Frank have distilled down years of learnings into quite a useful package. If you’re looking to get better at testing and validating ideas in the shortest amount of time (who isn’t?!), this is the book for you."

Hiten Shah, co-Founder of KISSMetrics, CrazyEgg, and Product Habits

"Every entrepreneur should read Testing with Humans and keep it nearby. It is an outstanding combination of readability, rigor and concrete action items for one of the most important and challenging thing every entrepreneur must do - define the right hypotheses, properly test them and maximize the learning in the process."

Professor Bill Aulet, MIT, author of Disciplined Entrepreneurship

"Entrepreneurs all know that they should talk to customers and run experiments, but that is easier said than done. This book does an excellent job making these concepts concrete and actionable."

Beth Ferreira, Partner, FirstMark Capital

"From my classroom at Carnegie Mellon to the boardroom of my VC investments, this book will join Talking to Humans as a critical resource helping those teams validate their ideas."

Sean Ammirati, VC and author of The Science of Growth

"Testing with Humans is a must read for every product team that wants to build the right thing. It’s a practical guide to experimentation, clearly explaining many types of experiments and breaking down exactly how to run them."

Melissa Perri, author of The Build Trap

"Giff and Frank have done it again. This practical, tactical book explains — to entrepreneurs, product managers and veteran practitioners alike — why you need to run experiments, how to do it and what to do with what you learn. It’s direct, concise and immediately useful. Read it this morning. Run your first experiment this afternoon."

Jeff Gothelf, author of Sense and Respond and Lean UX

"Testing with Humans is 70% practical, 30% inspirational, and 100% of it is stuff I wish I’d known 20 years ago."

Jeff Patton, author of User Story Mapping

"Entrepreneurs need confidence, but not arrogance. Entrepreneurial arrogance is an early warning sign of impending doom. Entrepreneurial confidence is based on an inquiring mind, that has beliefs, and is open to testing them. In this book Constable and Rimallovski guide us on a learning journey to test our entrepreneurial assumptions - the key to gaining true entrepreneurial confidence, mitigating risks and moving forward toward success."

Jerome Engel, U.C. Berkeley and Founding National Faculty Director, NSF I-Corps

"Testing with Humans fills a much-needed gap in the Lean Startup and innovation strategy world. Many espouse evidence-based testing approaches, but easier said than done — or taught. Until now."

Edmund Pendleton, Lead Instructor NSF and NIH I-Corps

What is in the book?

In 2014, we published Talking to Humans to help entrepreneurs learn how to speak directly with potential customers in order to vet and hone their ideas. Little did we know that the book would be read by many tens of thousands of people and picked up by leading universities, accelerators, and companies not just in the USA but around the world.

But customer discovery is not enough on its own. Talking with other people will give you the strongest leaps of inspiration and understanding, but experiments give you the strongest proof. An experiment is a test designed to help you answer the questions “Should we do this?” or “Am I right about this?” If you are open to learning, the insights from your experiments will help you refine your creation and improve your odds of success.

This book gives you concrete tactics, tools and examples to answer key questions:

  • Why run experiments?
  • When to test the business versus the product?
  • What makes a good experiment?
  • How do you turn experiments into decisions and actions?
  • How can we bring experiments into our business culture?

Where can you get the book?

You can purchase the book on Amazon, however if you are with a non-profit or educational organization, we share the book for free.

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Who is behind the book?


Giff Constable (giffconstable.com) is a repeat entrepreneur who has sold three companies and helped build many others. In 2014, he wrote the award-winning book Talking to Humans, in partnership with Frank Rimalovski, which is now standard reading in university and accelerator programs around the world. In 2018, they followed up with the sequel Testing with Humans. He led the globally recognized innovation consulting firm Neo as CEO until its acquisition by Pivotal, and personally led major projects at the Mayo Clinic and Time Inc., among others. He has held product and business roles across multiple startups, and provided M&A and IPO services to technology firms while at Broadview/Jefferies. He tries to give back to the entrepreneurial community whenever possible. He lives outside of New York City with his wife and two children.


Frank Rimalovski is an early-stage investor and entrepreneurship educator with over 25 years of experience in technology commercialization, startups and venture capital investing. He is the founding executive director of New York University’s Entrepreneurial Institute, and managing director of their Innovation Venture Fund. In 2014, he collaborated with Giff Constable to produce the award-winning book Talking to Humans. Frank currently serves as a mentor at TechStars, and teaches entrepreneurship at NYU’s Courant Institute. He has previously taught at the Tandon School of Engineering, and as an Instructor in the NSF’s I-Corps program, and has trained and mentored hundreds of entrepreneurs in customer development and lean startup methodologies. Previously, he was a founding partner of New Venture Partners, director/entrepreneur-in-residence at Lucent’s New Ventures Group, and has held various positions in product management, marketing and business development at Sun Microsystems, Apple and NeXT. He lives outside of New York City with his wife and his increasingly mellow mutt.