Contrary to popular belief, ecommerce is not just on the Web. In fact, ecommerce was alive and well in business to business transactions before the Web back in the 70s via EDI (Electronic Data Interchange) through VANs (Value-Added Networks). Ecommerce can be broken into four main categories: B2B, B2C, C2B, and C2C.
What is B2B e-commerce?
B2B e-commerce is simply defined as e-commerce between companies. This is the type of e-commerce that deals with relationships between and among businesses. About 80% of e-commerce is of this type, and most experts predict that B2B ecommerce will continue to grow faster than the B2C segment.
What is B2C e-commerce?
Business-to-consumer e-commerce, or commerce between companies and consumers, involves customers gathering information; purchasing physical goods (i.e., tangibles such as books or consumer products) or information goods (or goods of electronic material or digitized content, such 
as software, or e-books); and, for information goods, receiving products over an electronic network .
It is the second largest and the earliest form of e-commerce. Its origins can be traced to online retailing (or e-tailing) . Thus, the more common B2C business models are the online retailing companies such as Amazon.com, Drugstore.com, Beyond.com, Barnes and Noble and ToysRus. Other B2C examples involving information goods are E-Trade and Travelocity.
The more common applications of this type of e-commerce are in the areas of purchasing products and information, and personal finance management, which pertains to the management of personal investments and finances with the use of online banking tools.
What is C2C e-commerce?
Consumer-to-consumer e-commerce or C2C is simply commerce between private individuals or consumers.
This type of e-commerce is characterized by the growth of electronic marketplaces and online auctions, particularly in vertical industries where firms/businesses can bid for what they want from among multiple suppliers . It perhaps has the greatest potential for developing new markets.
This type of e-commerce comes in at least three forms: 
● auctions facilitated at a portal, such as eBay, which allows online real-time bidding
on items being sold in the Web;
● peer-to-peer systems, such as the Napster model (a protocol for sharing files
between users used by chat forums similar to IRC) and other file exchange and
later money exchange models; and
● classified ads at portal sites such as Excite Classifieds and eWanted .
What is C2B e-commerce?
A consumer posts his project with a set budget online and within hours companies review the consumer's requirements and bid on the project. The consumer reviews the bids and selects the company that will complete the project. Elance empowers consumers around the world by providing the meeting ground and platform for such transactions.
What is B2G e-commerce?
Business-to-government e-commerce or B2G is generally defined as commerce between companies and the public sector. It refers to the use of the Internet for public procurement, licensing procedures, and other government-related operations.
Web-based purchasing policies increase the transparency of the procurement process (and reduces the risk of irregularities). To date, however, the size of the B2G ecommerce market as a component of total e-commerce is insignificant, as government e-procurement systems remain undeveloped.
What is m-commerce?
M-commerce (mobile commerce) is the buying and selling of goods and services through wireless technology-i.e., handheld devices such as cellular telephones and personal digital assistants (PDAs). Japan is seen as a global leader in m-commerce. As content delivery over wireless devices becomes faster, more secure, and scalable, some believe that m-commerce will surpass wireline e-commerce as the method of choice for digital commerce transactions. Industries affected by m-commerce include:
● Financial services, including mobile banking (when customers use their
handheld devices to access their accounts and pay their bills), as well as brokerage
services (in which stock quotes can be displayed and trading conducted
from the same handheld device);
● Telecommunications, in which service changes, bill payment and account
reviews can all be conducted from the same handheld device;
● Service/retail, as consumers are given the ability to place and pay for orders
on-the-fly; and
● Information services, which include the delivery of entertainment, financial
news, sports figures and traffic updates to a single mobile device
