Career and employment counsellors are aware of the substantial changes in the labour market over the last two decades that are the result of complex, global influences. The labour market is dynamic and characterized by transition and elasticity as it responds to these forces. Workers need to adapt continually to changing career demands as some skills become obsolete and new ones are required. Lifelong learning is an essential component of work as individuals train and retrain to accommodate these skill shifts.

The National Occupational Classification (NOC), first published in 1993 and revised for Census 2001, was designed to reflect the effects of these pervasive changes in occupations and work. The NOC is the product of systematic, field-based research by Employment and Social Development Canada (ESDC). Its content and organization identify recent changes in the labour market and, along with its counselling component, the Career Handbook, provide information about occupations in Canada. A more detailed description of the development and revision of the NOC classification system and its structure is contained in the Introduction to NOC 2001.

Counsellors should note the difference between the definitions of an "occupation" and a "job" when using the NOC and the Career Handbook. An "occupation" is a theoretical concept which includes specific types of skills and responsibilities held in common by those who work in an occupation. A "job" on the other hand, is defined as a specific position in a particular establishment. An occupation is a collection of similar jobs. The list of example titles within each NOC unit group provides a frame of reference for the boundaries of that occupational group. The jobs within the group are characterized by a homogeneity or similarity of skills.

To make sense of current trends in the labour market, it is important to focus on occupations rather than jobs, and on skills rather than the specific tasks of individual jobs. Identifying the fundamental similarities of skills within an occupation allows users to examine concepts such as occupational mobility, transferability of skills and career shifts in today’s labour market.

To provide a complete representation of work in the Canadian economy, the NOC classifies occupations in major groups, according to two primary dimensions of skill – skill type and skill level. The major groups, which are identified by two-digit numbers, are then broken down further into minor groups with three-digit numbers and unit groups with four-digit numbers or codes. Within these three levels of classification, a unit group provides the actual profile of an occupation. The 2001 edition of the NOC contains descriptions for 520 occupations or unit groups.

The structure of the Career Handbook is identical to that of the NOC with one modification. In many cases, the NOC unit group has subgroup descriptions of Main Duties. In order to help users identify the differences between subgroups, the Career Handbook provides a unique occupational profile for each subgroup with a digit after a decimal point. For example, NOC unit group 5121 Writers, has three subgroups in its Main Duties section – Creative Writers, Technical Writers and Copywriters. In the Career Handbook, each of these subgroups has its own occupational profile – 5121.1 Creative Writers, 5121.2 Technical Writers and 5121.3 Copywriters. As a result, the Handbook contains 923 distinct groups derived from the 520 in NOC 2001.

For the purposes of this Introduction, each occupational group in the Career Handbook, whether an original NOC unit group or subgroup, is referred to as a group.