AU-C Section 220.18-19: Engagement Partner Review

AU-C Section 220.18-19 says:

".18 The engagement partner should take responsibility for reviews being performed in accordance with the firm's review policies and procedures. (Ref: par. .A15–.A16 and .A19)

.19 On or before the date of the auditor's report, the engagement partner should, through a review of the audit documentation and discussion with the engagement team, be satisfied that sufficient appropriate audit evidence has been obtained to support the conclusions reached and for the auditor's report to be issued. (Ref: par. .A17–.A19)"

QC Section 10 recommends that suitably experienced team members review the work of other team members.  As such, the engagement partner may delegate part of the review responsibility to other members of the engagement team.

A review consists of consideration of whether, for example

•  the work has been performed in accordance with professional standards and applicable legal and regulatory requirements;
•  significant findings or issues have been raised for further consideration;
•  appropriate consultations have taken place and the resulting conclusions
  have been documented and implemented;
• the nature, timing, and extent of the work performed is appropriate
  and without need for revision;
• the work performed supports the conclusions reached and is appropriately
  documented;
• the evidence obtained is sufficient and appropriate to support the
  auditor's report; and
• the objectives of the engagement procedures have been achieved.

Timely reviews by the engagement partner should the following items are appropriately addressed:

• Critical areas of judgment
• Significant risks
• Other areas that the engagement partner considers important

The engagement partner need not review all audit documentation; however, he must document
the extent and timing of the reviews as required by AU-C Section 230.

An engagement partner taking over an audit during the engagement may review the work performed to the date of the change in order to assume the responsibilities of an engagement partner.  

These direction, supervision, and review responsibilities are also required when the engagement team includes a member with expertise in a specialized area of accounting or auditing.  For example the engagement partner might

• Agree with that member upon the nature, scope, and objectives of that member's work and the respective roles of, and the nature, timing, and extent of communication between, that member and other members of the engagement team
•  Evaluate the adequacy of that member's work, including the relevance and reasonableness of that member's findings or conclusions and the consistency of those findings or conclusions with other audit evidence

https://www.aicpa.org/content/dam/aicpa/research/standards/auditattest/downloadabledocuments/au-c-00220.pdf