Exhibit 5.1

May 21, 2015

Communications Systems, Inc.

10900 Red Circle Drive

Minnetonka, Minnesota 55343

Ladies and Gentlemen:

This opinion is furnished in connection with the registration under the Securities Act of 1933 on Form S-8 of 1,100,000 shares of Common Stock, $.05 par value per share, of Communications Systems, Inc. (the “Company”) offered to employees, officers and directors of the Company or its subsidiaries pursuant to the Communications Systems, Inc. 2011 Executive Incentive Compensation Plan and the Communications Systems, Inc. 1990 Employee Stock Purchase Plan (the “Plans”).

As general counsel for the Company, we advise you that it is our opinion, based on our familiarity with the affairs of the Company and upon our examination of pertinent documents, that the 1,100,000 shares of Common Stock to be offered to employees, officers and directors under the Plans will, when paid for and issued, be validly issued and lawfully outstanding, fully paid and non-assessable shares of Common Stock of the Company.

The undersigned hereby consent to the filing of this opinion with the Securities and Exchange Commission as an Exhibit to the Registration Statement with respect to said shares of Common Stock under the Securities Act of 1933.

Very truly yours,

LINDQUIST & VENNUM LLP

/s/ Lindquist & Vennum LLP