"Association" in psychology refers to a connection between conceptual entities or mental states that results from the similarity between those states or their proximity in space or time. The idea stems from Plato and Aristotle, especially with regard to the succession of memories, and it was carried on by philosophers such as John Locke, David Hume, David Hartley, James Mill, John Stuart Mill, and Alexander Bain. It finds its place in modern psychology in such areas as conditioning and in neural network models of memory.
The following discussion assumes the point of view of associationistic theory. Some modern theorists disagree with this approach; they argue that it is very misleading to try to understand mental or brain function as a network of associations .
Memory seems to operate as as a chain of associations: concepts, words and ideas are interlinked, so that stimuli such as a person’s face calling up the name associated with the face. Understanding the relationships between different items is fundamental to episodic memory and damage to the hippocampal region of the brain has been found to hinder learning of associations between objects.
Pavlovian/Classical conditioning 
Classical conditioning is an example of associationistic learning. In his famous experiment, Pavlov paired the sound of a bell with food and later the dog salivated to the bell alone, indicating that an association had been established between the bell and food.
Operant conditioning 
In operant conditioning behaviors increase in strength and/or frequency when they have been followed by reward. This is theorized to follow from an association between the behavior and a mental representation of the food.
Implicit association 
Associations in humans can be measured with the Implicit Association Test, a psychological test which measures the implicit (subconscious) relation between two concepts. It has been used in investigations of subconscious racial bias. The test measures the associations between different ideas, such as race and crime. Reaction time is used to distinguish associations; faster reaction time is an indicator of a stronger association.
See also 
- Boring, E. G. (1950) "A History of Experimental Psychology" New York, Appleton-Century-Crofts
- Smith, E. E. & Kosslyn, S. M. (2007) "Cognitive Psychology: Mind and Brain", Upper Saddle River, New Jersey: Pearson/Prentice Hall
- Gallistel, C. R. & Gibbon, J. (2002) "The Symbolic Foundations of Conditioned Behavior" Mahwah New Jersey:Erlbaum.
- Watier & Collin 2012
- Gazzaniga, Ivry & Mangun, 2009
- Stark, Bayley & Squire, 2002
- Timberlake, 1994
- Shettleworth, S. J. (2010) "Cognition, Evolution and Behavior" New York, Oxford
- Greenwald, McGhee & Schwartz, 1998
- Crisp & Turner, R. N, R. J (2007). Attitude formation.In Essential social psychology. SAGE. p. 77.
- Gazzaniga, M. S., Ivry, R. B., & Mangun, G. R (2009). Learning and memory. In Cognitive neuroscience: The biology of the mind. W.W. Norton. p. 312.
- Greenwald, A. G; McGhee, D. E., & Schwartz, J. L. K. (1998). "Measuring individual differences in implicit cognition: The implicit association test". Journal of Personality and Social Psychology, 6 (74): 1464–1480.
- Stark, C. E. L; Bayley, P. J., & Squire, L. R. (2002). "Recognition memory for single items and for associations is similarly impaired following damage to the hippocampal region.". Learning & Memory 5 (9): 238–242. doi:10.1101/lm.51802.
- Timberlake, W (1994). "Behavior systems, associationism, and pavlovian conditioning.". Psychonomic Bulletin & Review 4 (1): 405–420.
- Watier, N.; Collin, C. (2012). "The effects of distinctiveness on memory and metamemory for face–name associations". Memory 1 (20): 73–88. doi:10.1080/09658211.2011.637935.
- Dictionary of the History of Ideas: Association of Ideas
- Time Associations: Associations we have with numbers on a digital clock
- Word Associations Network: The Word Association Dictionary