The assessment of a person’s work disability is among the key features of disability evaluation (DE). Disability evaluation is instrumental in assigning persons with disabilities (henceforth claimants) to appropriate return-to-work (RTW) programs, medical rehabilitation, and provision of assistive devices or medical devices. Providing the appropriate intervention for a particular person at the right time increases the cost-effectiveness of selected interventions, or, in other words, the chances for a successful outcome, namely, RTW [4]. RTW programs can be understood interchangeably with the term vocational rehabilitation (VR), which will be presented later in this chapter. An RTW program is in principle a process of VR for those who have previously worked with the ultimate goal of undertaking work duties in the long term. In the context of RTW, work disability can be understood as the inability to work due to an illness or injury in light of influencing contextual factors.

Disability evaluation is also crucial to determine a claimant’s eligibility for disability benefits as well as to establish appropriate levels of benefits. In addition, DE provides the necessary information to determine if the claimant should participate in an RTW program before receiving disability benefits. While there are differing definitions of disability evaluation toward eligibility determination for benefits [5–7], we refer to the “Medical Subject Headings” (MeSh) definition of DE: DE is the “determination of the degree of a person’s physical, mental, or emotional [disability]. The diagnosis is applied to legal qualification for benefits and income under disability insurance and to eligibility for Social Security and workers’ compensation benefits” [8]. In the context of eligibility determination for benefits, work disability is a legal concept with varying definitions among social security laws of different countries [9]. However, work disability usually refers to a person’s inability to work due to an illness or injury without considering the influence of contextual factors.

Disability evaluations should fulfill fundamental requirements to provide a just assignment to RTW programs as well as fair eligibility determination for disability benefits. The evaluations should be comparable in terms of content validity and inter-rater reliability between the medical experts who perform the assessments [10, 11]. This could be achieved with the introduction of standards in the disability evaluation process [12].

It is also essential that disability evaluation be documented in a transparent way [13, 14] and address how functional limitations at work are affected by the claimant’s health condition or by contextual factors. Moreover, the documentation should be plausible and comprehensible for all those involved in the disability evaluation process, including the medical experts, the claimants themselves, the legal system, and the disability insurance systems. To provide transparency, professional guidance on disability evaluation advises medical experts to capture a comprehensive picture of the claimants in their medical reports [15]. Such transparent documentations provide claimants with a basis for formally appealing eligibility decisions they deem as unwarranted.

Although different countries organize disability evaluation in varying ways, the key information in the evaluation usually refers to functioning and disability. Therefore, functioning assessments are a core element of disability evaluation [9] and provide important information for evaluating work disability. Functioning assessment in the context of disability evaluation address the claimant’s ability to perform activities relevant for executing physical or cognitive work tasks such as lifting or focusing attention. There are differences in functioning assessments depending on whether the sole purpose for the disability evaluation is determining eligibility for benefits, considering RTW, or both. Toward facilitating RTW, functioning assessments in disability evaluation focus on the appraisal of the performance of the claimant. The assessment of functional limitations or abilities and influencing contextual factors, such as the claimant’s living conditions or the job market situation, is the basis for selecting appropriate RTW programs to enhance the claimant’s potential to perform work tasks and subsequent work participation. Functioning assessment in the context of determining eligibility for benefits is geared toward an objective statement about the claimant’s functional capacity in a standardized environment without considering the influence of contextual factors. The functioning assessment provides key information on the relationship between impairments and functional limitations and thus ascertains a claimant’s work disability.

When a worker becomes ill or develops a health condition or disease, work disability may result which can prevent the individual from continuing to work. Work disability may be associated with personal suffering, limitations in functioning, loss of income, high medical costs, and strained relationships of the individual with others. In addition, work disability may lead to diminished productivity for the individual as a member of society.