People are always talking about the latest viral video, viral music, viral ad, viral meme, viral anything. What does “viral” mean in this context anyway? Simply put, when something has gone “viral”, it is being rapidly circulated around the Internet. For online marketers, viral is the goal. Viral means that the idea, product, service, or campaign has “stuck”. It means raking in web hits and profits.

Here are six books about viral marketing that you should read now for online marketing success.

#1: Contagious: Why Things Catch On

Jonah Berger answers the big marketing question: “What makes a thing popular?” This highly informative book combines groundbreaking research with true-to-life marketing scenarios to explain the phenomena that make things contagious.

#2: Predictably Irrational, Revised & Expanded Edition: The Hidden Forces that Shape Our Decisions

Why do we spend lavishly on our morning coffee and then scrimp on lunch? Why do some things somehow look, feel, and smell better just because they’re more expensive? Why do we keep watching that same video even when we know it’s completely dumb? In this fascinating book, Dan Ariely explains the rationality behind behaviors that seem completely irrational.

#3: Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives: How Your Friends’ Friends’ Friends Affect Everything You Feel, Think, and Do

Nicholas A. Christakis and James H. Fowler offer scientific answers and provide persuasive evidence on how we influence each other’s tastes, happiness, health, wealth, and beliefs. They also explain how social networks develop and how they operate.

#4: Made to Stick: Why Some Ideas Survive and Others Die

How can brands tell a better story? That is the question that Chip Heath and Dan Heath answer in Made to Stick. Read about how people with important ideas can get their ideas to “stick” and how ideas can be made “stickier.” If you have a good business idea or a new product and you want to know how to market it successfully, read this.

#5: Viral Loop: From Facebook to Twitter, How Today's Smartest Businesses Grow Themselves

In Viral Loop, Adam L. Penenberg tells the stories of the entrepreneurs who first utilized what he calls “the viral loop” and thus gave rise to some of the biggest, most game-changing companies we know today – YouTube, Twitter, Flickr, eBay, and others. According to Penenberg, to use it, you have to spread it. He then offers tips on how we can utilize the paradigm-busting effect of viral loops to grow our businesses via technology.

#6: Word of Mouth Marketing: How Smart Companies Get People Talking

Using examples from some of the world’s biggest companies and how they gain their biggest customers through word of mouth marketing, Andy Sernovitz offers fun and useful tips on how to employ the principles that make social media, evangelism, and viral marketing work. He dishes practical techniques on honest marketing, how to get people to talk about your product, and how to implement a promotional campaign without spending a dime.