What is Significance?
The concept of significance is important in a number of fields, especially statistics.
In cultural heritage the identification and understanding of the various elements of a site or structure, of a collection, or of an object, has long been a routine preliminary step to understanding and then differentiating between examples.
The significance concept came to be incorporated into national legislation for built and archaeological heritage in a number of countries by the early twentieth century, for example the United States Historic Sites Act (1935) and later in UNESCO Conventions. 
Managerial frameworks erected around the concept differ from place to place, with the most successful resource for built and archaeological heritage arguably being the International Council on Monuments and Sites (ICOMOS) The Burra Charter, 1979.
In the 1990’s great steps toward the better understanding and definition of significance for movable cultural heritage (as opposed to value(s)) were taken in two countries.
In the Netherlands the ‘Delta Plan Project for the Preservation of Cultural Heritage’ sought to identify and classify every built and movable item of cultural heritage, primarily for conservation/preservation purposes. The Netherlands continues to work on the results of their determinations today.
In Australia, discussion and testing workshops around the country led to the creation of an openly structured consensus definition of significance, and an accompanying assessment framework.
Pioneers of the Australian work were heritage consultant Kylie Winkworth, historian Roslyn Russell, and academics Stephen Foster and Linda Young. Results of this work were published as [significance]: a guide to assessing the significance of cultural heritage objects and collections (2001) [.pdf download 2.5MB], by R. Russell and K. Winkworth for the Heritage Collections Council and the Commonwealth of Australia. This well received edition focuses on the assessment of single items and on the significance criteria. It defines significance as follows:
Significance means the historic, aesthetic, scientific and social values that an object or collection has for past, present and future generations. 
In response to popular demand the Collections Council of Australia (descendent of the Heritage Collections Council) freshly commissioned Russell and Winkworth to prepare a second edition of the work, in light of their own experience since 2001 and in response to a set of requirements from the funding partner (the Commonwealth of Australia) and publisher/project manager, the Collections Council of Australia.
The second edition Significance 2.0: a guide to assessing the significance of collections [archived webpage - click through, also .pdf download 3.8 MB] was originally published online and in print in May 2009 (please see Note below). Similar to the distribution of the first edition, a total of 2,900 copies of the second edition were provided free of charge to Australian collecting organisations. In this edition:
Significance refers to the values and meanings that items and collections have for people and communities. Significance helps unlock the potential of collections, creating opportunities for communities to access and enjoy collections, and to understand the history, cultures and environments of Australia. 
Significance 2.0 focuses on the assessment of whole collections and the process of assessing significance. Click here to see the summary 10-step process recommended by the authors [click through to archived webpage].
This edition also highlights critical concepts associated with significance assessment such as provenance, context, and collections that are held across different collecting organisation types e.g. archives, libraries and museums.
Russell and Winkworth also slightly refined the significance criteria as follows:
Primary criteria: historic significance
artistic or aesthetic significance
scientific or research significance
social or spiritual significance
Comparative criteria: provenance
rarity or representativeness
condition or completeness
Essentially, the significance assessment method remains unchanged between the two editions: ‘It still hinges on the preparation of a well-researched ‘statement of significance’, which references a set of primary and comparative criteria.’ 
At Significance International we use and teach the definitions and assessment method recommended in Significance 2.0: a guide to assessing the significance of collections (2010) [archived website - click through; .pdf download 3.8 MB].
Click here to read about the Significance Assessment Workshop held by Significance International in November 2010.
Significance 2.0 was a 2009 publication of the Collections Council of Australia, but with closure of the Council in early 2010 custodianship transferred to the Commonwealth of Australia. The free online publication was 're-launched' by the Commonwealth on one of its websites in early October 2010. Now copyrighted to the Commonwealth of Australia the online publication is available at: http://www.environment.gov.au/heritage/publications/significance2-0/.
 Two relevant UNESCO Conventions contain the term ‘significance’: Convention concerning the Protection of the World Cultural and Natural Heritage, 1972; and the Convention on the Protection of Underwater Cultural Heritage, 2001; while the two other most relevant UNESCO Conventions do not contain the term ‘significance’, however significance is implied: Convention for the Protection of Cultural Property in the Event of Armed Conflict 1954, and Second Protocol 1999; and Convention on the Means of Prohibiting and Preventing the Illicit Import, Export and Transfer of Ownership of Cultural Property, 1970.