Attachment measures refer to the various procedures used to assess attachment in children and adults.
Researchers have developed various ways of assessing attachment in children, including the Strange Situation and story-based approaches such as Attachment Story Completion Test. These methods allow children to be classified into four attachment styles: secure, anxious-ambivalent, anxious-avoidant, and disordered. Attachment in adults is commonly measured using the Adult Attachment Interview and self-report questionnaires. Self-report questionnaires have identified two dimensions of attachment, one dimension dealing with anxiety about the relationship, and the other dimension dealing with avoidance in the relationship. These dimensions define four styles of adult attachment: secure, preoccupied, dismissive-avoidant, and fearful-avoidant.
Measuring Attachment in Children
Researchers have developed several ways to assess attachment in children.
The Strange Situation
Mary Ainsworth is a developmental psychologist who devised a procedure called The Strange Situation, to observe attachment relationships between a human caregiver and child.  In this procedure the child is observed playing for 20 minutes while caregivers and strangers enter and leave the room, recreating the flow of the familiar and unfamiliar presence in most children's lives. The situation varies in stressfulness and the child's responses are observed. The child experiences the following situations:
- Mother and baby enter room.
- Mother sits quietly on a chair, responding if the infant seeks attention.
- A stranger enters, talks to the mother then gradually approaches infant with a toy. The mother leaves the room.
- The stranger leaves the infant playing unless he/she is inactive and then tries to interest the infant in toys. If the infant becomes distressed this episode is ended.
- Mother enters and waits to see how the infant greets her. The stranger leaves quietly and the mother waits until the baby settles, and then she leaves again.
- The infant is alone. This episode is curtailed if the infant appears to be distressed.
- The stranger comes back and repeats episode 3.
- The mother returns and the stranger goes. Reunion behaviour is noted and then the situation is ended.
Two aspects of the child's behaviour are observed:
- The amount of exploration (e.g. playing with new toys) the child engages in throughout, and
- The child's reactions to the departure and return of its caregiver.
Narrative and story-stem approaches are often used with older toddlers, children, and teens to determine their state of mind with respect to attachment. The Attachment Story Completion Test is one such methodology.
However, it should be noted that existing measures have not necessarily been developed to a useful level. "Behavioral observation is a natural starting point for assessing attachment disorders because behavioral descriptions... have been central to the development of the concept... despite the fact that observations have figured prominently... no established observational protocol has been established" [citation O'Connor, T., & Zeanah, C.H. (2003)."Attachment disorders: Assessment strategies and treatment approaches." Attachment & Human Development, 5(3):223-244, p. 229].
Measuring Attachment in Adults
The two main ways of measuring attachment in adults include the Adult Attachment Interview (AAI) and self-report questionnaires. The AAI and the self-report questionnaires were created with somewhat different aims in mind. Shaver and Fraley note:
"If you are a novice in this research area, what is most important for you to know is that self-report measures of romantic attachment and the AAI were initially developed completely independently and for quite different purposes. One asks about a person's feelings and behaviors in the context of romantic or other close relationships; the other is used to make inferences about the defenses associated with an adult's current state of mind regarding childhood relationships with parents. In principle, these might have been substantially associated, but in fact they seem to be only moderately related--at least as currently assessed. One kind of measure receives its construct validity mostly from studies of romantic relationships, the other from prediction of a person's child's behavior in Ainsworth's Strange Situation. Correlations of the two kinds of measures with other variables are likely to differ, although a few studies have found the AAI to be related to marital relationship quality and a few have found self-report romantic attachment measures to be related to parenting." (Shaver & Fraley, 2004) 
The AAI and the self-report questionnaires offer distinct, but equally valid, perspectives on adult attachment. It's therefore worthwhile to become familiar with both approaches.
Adult Attachment Interview (AAI)
Developed by Mary Main and her colleagues, this is a semi-structured interview that takes about one hour to administer. It involves about twenty questions and has extensive research validation to support it. A good description can be found in Chapter 19 of Attachment Theory, Research and Clinical Applications, edited by J. Cassidy and P. R. Shaver, Guilford Press, NY, 1999. The chapter title is "The Adult Attachment Interview: Historical and Current Perspectives," and is written by E. Hesse.
Some of the strongest external validation of the measures involves its demonstrated ability to predict interviewees' childrens' classifications in the Strange Situation. The measure also has shows to have some overlap with attachment constructs measured by the less time-intensive measures of the peer/romantic attachment tradition (Hazan & Shaver, Bartholomew), as reported by Shaver, P. R., Belsky, J., & Brennan, K. A. (2000). However, it should be noted that there are important differences in what is measured by the AAI--rather than being a measure of romantic attachment, it taps primarily into a person's state of mind regarding their attachment in their family of origin (nuclear family).
Hazan and Shaver created the first questionnaire to measure attachment in adults.  Their questionnaire was designed to classify adults into the three attachment styles identified by Ainsworth. The questionnaire consisted of three sets of statements, each set of statements describing an attachment style:
- Secure - I find it relatively easy to get close to others and am comfortable depending on them and having them depend on me. I don't often worry about being abandoned or about someone getting too close to me.
- Avoidant - I am somewhat uncomfortable being close to others; I find it difficult to trust them completely, difficult to allow myself to depend on them. I am nervous when anyone gets too close, and often, love partners want me to be more intimate than I feel comfortable being.
- Anxious/Ambivaent - I find that others are reluctant to get as close as I would like. I often worry that my partner doesn't really love me or won't want to stay with me. I want to merge completely with another person, and this desire sometimes scares people away.
People participating in their study were asked to choose which set of statements best described their feelings. The chosen set of statements indicated their attachment style. Later versions of this questionnaire presented scales so people could rate how well each set of statements described their feelings.
One important advance in the development of attachment questionnaires was the addition of a fourth style of attachment. Bartholomew and Horowitz presented a model that identified four categories or styles of adult attachment.  Their model was based on the idea attachment styles reflected people's thoughts about their partners and thought about themselves. Specifically, attachment styles depended on whether or not people judge their partners to be generally accessible and responsive to requests for support, and whether or not people judge themselves to be the kind of individuals towards which others want to respond and lend help. They proposed four categories based on positive or negative thoughts about partners and on positive or negative thoughts about self.
Bartholomew and Horowitz used this model to create the Relationship Questionnaire (RC). The RC consisted of four sets of statements, each describing a category or style of attachment:
- Secure - It is relatively easy for me to become emotionally close to others. I am comfortable depending on others and having others depend on me. I don't worry about being alone or having others not accept me.
- Dismissive - I am comfortable without close emotional relationships. It is very important to me to feel independent and self-sufficient, and I prefer not to depend on others or have others depend on me.
- Preoccupied - I want to be completely emotionally intimate with others, but I often find that others are reluctant to get as close as I would like. I am uncomfortable being without close relationships, but I sometimes worry that others don't value me as much as I value them.
- Fearful - I am somewhat uncomfortable getting close to others. I want emotionally close relationships, but I find it difficult to trust others completely, or to depend on them. I sometimes worry that I will be hurt if I allow myself to become too close to others.
Tests demonstrated the four attachment styles were distinct in how they related to other kinds of psychological variables. Adults indeed appeared to have four styles of attachment instead of three attachment styles.
David Schmitt, together with a large number of colleagues, validated the attachment questionnaire created by Bartholomew and Horowitz in 62 cultures.  The distinction of thoughts about self and thoughts about partners proved valid in nearly all cultures. However, the way these two kinds of thoughts interacted to form attachment styles varied somewhat across cultures. The four attachment styles had somewhat different meanings across cultures.
A second important advance in attachment questionnaires was the use of independent items to assess attachment. Instead of asking people to choose between three or four sets of statements, people rated how strongly they agreed with dozens of individual statements. The ratings for the individual statements were combined to provide an attachment score. Investigators have created several questionnaires using this strategy to measure adult attachment.
Two popular questionnaires of this type are the Experiences in Close Relationships (ECR) questionnaire and the Experiences in Close Relationships - Revised (ECR-R) questionnaire. The ECR was created by Brennan, Clark, and Shaver in 1998.  The ECR-R was created by Fraley, Waller, and Brennan in 2000.  Readers who wish to take the ECR-R and learn their attachment style can find an online version of the questionnaire at http://www.web-research-design.net/cgi-bin/crq/crq.pl.
Analysis of the ECR and ECR-R reveal that the questionnaire items can be grouped into two dimensions of attachment. One group of questionnaire items deal with how anxious a person is about their relationship. These items serve as a scale for anxiety. The remaining items deal with how avoidant a person is in their relationship. These items serve as a scale for avoidance. Many researchers now use scores from the anxiety and avoidance scales to perform statistical analyses and test hypotheses.
Scores on the anxiety and avoidance scales can still be used to classify people into the four adult attachment styles.    The four styles of attachment defined in Bartholomew and Horowitz's model were based on thoughts about self and thoughts about partners. The anxiety scale in the ECR and ECR-R reflect thoughts about self. Attachment anxiety relates to beliefs about self-worth and whether or not one will be accepted or rejected by others. The avoidance scale in the ECR and ECR-R relates to thoughts about partners. Attachment avoidance relates to beliefs about taking risks in approaching or avoding other people. Combinations of anxiety and avoidance can thus be used to define the four attachment styles. The secure style of attachment is characterized by low anxiety and low avoidance; the preoccupied style of attachment is characterized by high anxiety and low avoidance; the dismissive avoidant style of attachment is characterized by low anxiety and high avoidance; and the fearful avoidant style of attachment is characterized by high anxiety and high avoidance.
- Ainsworth. Mary D. (1978) Patterns of Attachment: A Psychological Study of the Strange Situation. Lawrence Erlbaum Associates. ISBN 0-89859-461-8.
- Shaver, P.A. & Fraley, R.C. (2004). Self-report measures of adult attachment. Online article. Retrieved June 20, 2006, from http://www.psych.uiuc.edu/~rcfraley/measures/measures.html .
- Shaver, P. R., Belsky, J., & Brennan, K. A. (2000). The adult attachment interview and self-reports of romantic attachment: Associations across domains and methods. Personal Relationships, 7, 25-43.
- Hazan, C., & Shaver, P. (1987). Romantic love conceptualized as an attachmenpt process. Journal of Personality and Social Psychology, 52, 511-524.
- Bartholomew, K. & Horowitz, L.M. (1991). Attachment styles among young adults: A test of a four-category model. Journal of Personality and Social Psychology, 61, 226-244.
- Schmitt, D.P., et al. (2004). Patterns and universals of adult romantic attachment across 62 cultural regions. Journal of Cross-Cultural Psychology, 35, 367-402.
- Brennan, K.A., Clark, C.L., & Shaver, P.R. (1998). Self-report measurement of adult romantic attachment: An integrative overview. In J.A. Simpson & W.S. Rholes (Eds.), Attachment theory and close relationships (pp. 46-76). New York: Guilford Press.
- Fraley, R.C., Waller, N.G., & Brennan, K.A. (2000). An item-response theory analysis of self-report measures of adult attachment. Journal of Personality and Social Psychology, 78, 350-365.
- Bartholomew, K. & Shaver, P.R. (1998). Methods of assessing adult attachment. In J. A. Simpson & W. S. Rholes (Eds.), Attachment theory and close relationships, pp. 25-45. New York, NY: Guilford Press.
- Collins, N.L. & Freeney, B.C. (2004). An Attachment Theory Perspective on Closeness and Intimacy. In D.J. Mashek & A. Aron (Eds.), Handbook of Closeness and Intimacy, pp. 163-188. Mahwah, NJ: Lawrence Erlbaum Associates.
- Becker-Weidman, A., & Shell, D., (Eds). (2005) Creating Capacity for Attachment Wood N Barnes, Oklahoma City, OK. ISBN 1-885473-72-9
- Cassidy, J., & Shaver, P., (Eds). (1999) Handbook of Attachment: Theory, Research, and Clinical Applications. Guilford Press, NY.
- Greenberg, MT, Cicchetti, D., & Cummings, EM., (Eds) (1990) Attachment in the Preschool Years: Theory, Research and Intervention University of Chicago, Chicago.
- Greenspan, S. (1993) Infancy and Early Childhood. Madison, CT: International Universities Press. ISBN 0-8236-2633-4.
- Holmes, J. (1993) John Bowlby and Attachment Theory. Routledge. ISBN 0-415-07730-3.
- Holmes, J. (2001) The Search for the Secure Base: Attachment Theory and Psychotherapy. London: Brunner-Routledge. ISBN 1-58391-152-9.
- Karen R (1998) Becoming Attached: First Relationships and How They Shape Our Capacity to Love. Oxford University Press. ISBN 0-19-511501-5.
- Parkes, CM, Stevenson-Hinde, J., Marris, P., (Eds.) (1991) Attachment Across The Life Cycle Routledge. NY. ISBN 0-415-05651-9
- Siegler R., DeLoache, J. & Eisenberg, N. (2003) How Children develop. New York: Worth. ISBN 1-57259-249-4.
- Sturt, SM (Ed) (2006). New Developments in Child Abuse Research Nove, NY. ISBN 1-59454-980-X
- AICAN - Australian Intercountry Adoption Network
- Information on effective treatment for attachment disorders and training for professionals. Information on Dyadic Developmental Psychotherapy
- Parenting: Attachment, Bonding and Reactive Attachment Disorder
- Relationship Advice: How Understanding Adult Attachment Can Help
- Attachment Questionnaire
- Articles on attachment measures including 11 self-report measures with scoring instructions