There's no part of the business world that's evolving faster than marketing. Fifteen years ago, websites were just online brochures. Ten years ago, SEO was a brand new concept. Five years ago, free-to-play, the sharing economy, and content marketing--to name just a few--didn't exist.

Marketing is experiencing "disruptive innovation" on steroids, which is why it's essential for entrepreneurs and marketers alike to keep abreast of the new ideas and techniques that continue to emerge. These five newly-published books are the best and most essential of the hundreds of marketing books published this year:

1. Ask

Subtitle: The Counterintuitive Online Formula to Discover Exactly What Your Customers Want to Buy...Create a Mass of Raving Fans...and Take Any Business to the Next Level

Author: Ryan Levesque

Key Takeaway: Ad and website copy must be written to be interactive and lead the customer towards a purchase rather than simply a dump of information or a static attempt to create emotion.

Best Quote: "Four surveys--and the four big questions they represent--are foundational to the Ask Formula because they are key to finding out exactly what your customers want to buy. If you don't know what the customer wants (or you assume you know what they want), there might be a mismatch between how you're positioning your product and what the market really wants. Even worse, you might be offering the wrong products or services altogether--both of which ultimately lead to losing sales."

2. Traction

Subtitle: How Any Startup Can Achieve Explosive Customer Growth

Authors: Gabriel Weinberg and Justin Mares

Key Takeaway: Use a mix of marketing methods to build a customer base and have successive products in development long before they're needed to maintain and increase momentum.

Best Quote: "Traction is a sign that your company is taking off. It's obvious in your core metrics: if you have a mobile app, your download rate is growing rapidly. If you're running a subscription service, the monthly revenue is skyrocketing. If you're an organic bakery, your number of transactions is increasing every week. The point of a startup is to grow rapidly. Getting traction means moving your growth curve up and to the right as best you can. Traction is growth. The pursuit of traction is what defines a startup."

​3. DotCom Secrets

Subtitle: The Underground Playbook for Growing Your Company Online

Author: Russell Brunson

Key Takeaway: Define your ideal customer, figure out where such customers hang out on the Web, offer them something that they want, and your company will grow apace.

Best Quote: "This may seem like a silly exercise, but it's important that you do it anyway. Really spend some time thinking about who you want to work with. Write out their characteristics and then go find an actual picture to represent them. It's amazing how your perspective changes when you have a physical picture of your ideal customer--instead of a hazy half-formed image in your head."

4. The Membership Economy

Subtitle: Find Your Superusers, Master the Forever Transaction, and Build Recurring Revenue

Author: Robbie Kellman Baxter

Key Takeaway: Customers remain loyal and buy more from you if you can entice them into thinking of themselves as members of a limited-access club with members who share the same values.

Best Quote: "Membership is timeless, important, and powerful. People crave it. My town has a neighborhood of closely packed houses, designed to look like 'small town America.' The development forbids tall front yard fences and gates, sidewalks abound, and there's even a small 'neighborhood' park. A few blocks away, in an equally convenient and prestigious area, is a second neighborhood with bigger yards and bigger houses, but people pay the same amount as they do for the privilege of living in the smaller houses in the stronger community. In other words, people seem to be willing to pay a premium for a connection, for a neighborhood. They are willing to give up privacy in exchange for association with others. A membership organization builds a 'neighborhood' for its ideal customer. There's a cost associated with both buying and maintaining a house in a neighborhood, so the promise of connection, community, and ongoing value must be guaranteed."

5. The Content Code

Subtitle: Six Essential Strategies to Ignite Your Content, Your Marketing, and Your Business

Author: Mark W. Schaefer

Key Takeaway: Content marketing is useless unless and until the intended audience is willing to share it with other people.

Best Quote: "I want to be clear that sharing is different than a 'Like,' a comment, or a 'Plus 1.' Content transmission is what you're after. Spreading the word. Building the buzz. It may be true that most frequently shared posts also get a lot of Likes and comments, and there are also many posts that are frequently Liked but barely shared. A leading reason that posts can be Liked but not shared is that a person may Like a post to support a political, theological, or philosophical view that may upset a general audience if it is transmitted broadly. We generally don't want to make people uncomfortable, so we don't always share."

Coming Soon: The 10 Best Business Books of 2015

Every year, I name the best business books in multiple categories and then (this year on December 15), I name the best of the best. In addition to this post, here are the categories so far:

Stay tuned for the finale on December 15!