Project managers need to have a good understanding of the communication process. What follows is a high-level description that occurs on group and person-to-person levels.
All communication has a sender and a receiver. The sender develops and forwards a message to a receiver who interprets it and makes a decision based on the contents. At first glance, it appears this is a simple one-way process; but, in reality, it is not. The receiver responds or reacts to the message reflected in a signal that he or she returns to the sender in the form of feedback. This exchange can occur many times under different situations according to some signal.
What happens during this exchange is that both parties are encoding and decoding based on factors like perceptions, values, and emotional states. The messages exchanged then get modified according to interpretation.
The exchange of messages can occur over different media or channels. For example, a sender may elect to communicate a message through oral communication and the receiver may respond in the same mode or through e-mail. Each medium has its pluses and minuses. Sometimes, a message is distorted by the medium through noise, or interference, when being transmitted.
Of course, several quantitative and qualitative characteristics of messages affect their preparation and processing by sender and receiver. These characteristics include load, timing, format, speed, and familiarity . While transmitting a message, too many factors can affect it. These include distortion, lag and lead times, and influence of the channel or medium.
However, other factors are often overlooked that can add barriers to communicating by filtering or "massaging" the messages. These factors include culture, perceptions, trust, organizational climate, history, role expectations, ethnicity , psychological motivations, and power of people in responsible positions .
Not surprisingly, therefore, the intent and meaning of a message can get modified or lost. Fortunately, feedback plays an important role. Sender and receiver alike can exchange signals verifying whether a message has or has not been properly received and acted on as intended.
Communication can also occur on different planes. It can occur formally or informally. For example, it can occur via documentation, e.g., reports or memorandums, or by casual one-on-one discussions with stakeholders without any recordkeeping. Communication can occur verbally and nonverbally. An example of a verbal level is a presentation or e-mail. An example of a nonverbal communication is body language. Communication can also be in oral and written form. An example of the former is a presentation; for the latter, a report.
Communication can flow in different directions. It can move in a downward direction, e.g., from management to the rank and file; upward, e.g., from the team to the senior management; and laterally, e.g., among team members .
The ultimate goal is that a sender wants to ensure that a message sent is the one received by the recipient and in the manner intended. In Human Communication , Stewart Tubbs and Sylvia Moss write that the success of communication occurs when the intent matches the intended response.  Douglas Benton agrees but in a more practical way, noting that successful communication is reflected by whether a message is understood .  From a project management perspective, effective communication results when a message is understood as intended and mutually engages both sender and receiver. 
 Stewart L. Tubbs and Sylvia Moss, Human Communication , 8th ed., McGraw-Hill, Boston, 2000, p. 20.
 Douglas A. Benton, Applied Human Relations , 6th ed., Prentice Hall, Englewood Cliffs, NJ, 1998, p. 194.
 Michelle Keiserman, Project team communications: the grease, the glue and the...gum? PM Network , p. 17, May 1999.