Language Barriers
Clearly, language and linguistic ability may act as a barrier to communication.  However, even when communicating in the same language, the terminology used in a message may act as a barrier if it is not fully understood by the receiver(s).  For example, a message that includes a lot of specialist jargon and abbreviations will not be understood by a receiver who is not familiar with the terminology used. Regional colloquialisms and expressions may be misinterpreted or even considered offensive. See our page: Effective Speaking for more information.
Psychological Barriers
The psychological state of the receiver will influence how the message is received.  For example, if someone has personal worries and is stressed, they may be preoccupied by personal concerns and not as receptive to the message as if they were not stressed.  Stress management is an important personal skill that affects our interpersonal relationships. See our pages Stress: Symptoms and Triggers and Avoiding Stress for more information.
Anger is another example of a psychological barrier to communication, when we are angry it is easy to say things that we may later regret and also to misinterpret what others are saying. See our pages: What is Anger?, Anger Management and Anger Management Therapy for more information. More generally people with low self-esteem may be less assertive and therefore may not feel comfortable communicating - they may feel shy about saying how they really feel or read negative sub-texts into messages they hear. Visit our pages on Improving Self-Esteem and Assertiveness for more information.
Physiological Barriers
Physiological barriers may result from the receiver’s physical state: for example, a receiver with reduced hearing may not grasp to entirety of a spoken conversation especially if there is significant background noise.
Physical Barriers
An example of a physical barrier to communication is geographic distance between the sender and receiver(s).  Communication is generally easier over shorter distances as more communication channels are available and less technology is required. Although modern technology often serves to reduce the impact of physical barriers, the advantages and disadvantages of each communication channel should be understood so that an appropriate channel can be used to overcome the physical barriers.  
Systematic Barriers
Systematic barriers to communication may exist in structures and organisations where there are inefficient or inappropriate information systems and communication channels, or where there is a lack of understanding of the roles and responsibilities for communication. In such organisations, individuals may be unclear of their role in the communication process and therefore not know what is expected of them.
Attitudinal Barriers
Attitudinal barriers are behaviours or perceptions that prevent people from communicating effectively.  Attitudinal barriers to communication may result from personality conflicts, poor management, resistance to change or a lack of motivation.  Effective receivers of messages should attempt to overcome their own attitudinal barriers to facilitate effective communication.