The similarities between the internal and external OD practitioners is that both have to consider and abide by the OD Code of Ethics and be aware of the three types of dilemmas in organizational diagnosis and learn how to operate and display  best practices in these situations (goals, politics and professionalism dilemmas).

Also, both internal and external OD consultants need to manage the time required before collecting data, understand the best ways to manage communications efforts with their clients, have strong credibility and engage stakeholders, manage time, and ensure OD competencies are apparent to clients. However, internal and external OD consultants have differences in the areas listed above in this paragraph.

For example an external OD consultant may take a lot of time to understand the organization where internal OD consultants have a stronger understand being an insider of the organization.

Internal OD consultants can communicate progress on their own and with organization key stakeholders, who they already have connections to. External OD consultants need to rely on organization internal members to communicate progress.

An advantage external OD consultants have is that they are often seen as more credible up front, where internal OD consultants are often building their credibility within organizations.

Internal OD consultants can  more quickly make their activities relevant and engage key stakeholder in organizations. External OD consultants have to prove more relevance of diagnostic activities with organization stakeholders.

Both internal and external OD consultants have issues of time management and quality however with external consultants they may have challenges of working with multiple clients (different organizations) where internal consultants may have other responsibilities outside of the OD activity at hand to manage in their work load within their own organization.

External OD consultants are effective at demonstrating their OD competencies however they must be sure to understand the specific competencies needed from their clients and asses if their competencies are a match for the client’s needs. Internal OD consultants build their competencies as they take on new OD projects in their organization (unless their work is already centered on OD). Therefore, internal OD consultants are encouraged to partner with other (both internal and external) consultants to continue to build competencies.