The Communist Manifesto, first published in 1848 for the Communist League, had little influence in its own day. Only after Karl Marx and Friedrich Engels' other writings had made their views on socialism widely known did it become a standard text. For about a century it was one of the most widely read (and some would argue misread) documents in the world.
But why study it today? Most of the communist world has collapsed. Nominally communist countries like Vietnam and China are busily building market economies in defiance of everything Marx advocated, and Korea and Cuba are barely surviving, serving as models for no one. Has not Marxism been relegated to the ash-heap of history?
There are several reasons why The Communist Manifesto is still an important document. As a historically significant work, it has a certain intrinsic interest. It is good to know what the great ideas are which have shaped history. Some people would argue that Marxists so thoroughly betrayed Marxism that the document can be used to show why attempts at building communist states failed: they were never truly Marxist at all. If true Marxism has never been tried, then it might be worth reconsidering afresh. Or if, as others argue, Marxism has intrinsic flaws that doomed it from the beginning, we might hope to discover traces of them here which might teach us why Marxism should be shunned. The goal here is not to convert you, but to help you explore Marx's writing from his point of view, so that you can understand his actual meaning while still maintaining a stance that can allow you to think critically about the subject and form your own opinions.
It is important to understand that Marx played two important roles in world history: as a critic of capitalism and as an advocate of socialism. He actually wrote very little on the latter subject. Although a strong believer in the importance of building socialism, he spent most of his time and energy on a subtle and complex critique of the capitalist system. This critique is still very influential on many historians, art and literature scholars, sociologists and others. There have been many neo-Marxisms which have been based more or less loosely on the original ideas of Marx and which are widely discussed today. Whether you want to explore such ideas or combat them, it's good to have some notion of the subject.
A manifesto is a document which proclaims publicly--or makes manifest-- the central ideas of a group or individual. Although the organization for which this one was written was underground (for the simple reason that it was illegal) Marx always envisioned the socialist movement as open. He rejected secret conspiracies because his ideal of building socialism was envisioned as a majority enterprise which could only accumulate the necessary momentum through an open, broadly-based campaign of education and exhortation.
Engels was Marx's close collaborator and an important thinker and writer in his own right. He outlived Marx by many years, and produced several volumes which are still influential. Marx was clearly the more powerful thinker of the two, but Engels was the better stylist. Although Engels may have been responsible for much of the eloquent writing in the Manifesto, because it incorporates Marx's ideas and embodies some central concepts of what came to be known as Marxism the following questions will refer to the authors simply as "Marx."