================================================================================

     As filed with the Securities and Exchange Commission on April 27, 2001

                                               Registration No. 333-____________

                UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8

             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
                                _________________

                      TRANSACTION SYSTEMS ARCHITECTS, INC.
             (Exact name of registrant as specified in its charter)

              Delaware                              47-0772104
    (State or other jurisdiction of      (I.R.S. Employer Identification No.)
     incorporation or organization)

                             224 South 108th Avenue
                              Omaha, Nebraska 68154
          (Address of principal executive offices, including zip code)
                                _________________

           Transaction Systems Architects, Inc. 1999 Stock Option Plan
     Transaction Systems Architects, Inc. 1999 Employee Stock Purchase Plan
                            (Full title of the plans)

                              David P. Stokes, Esq.
                          General Counsel and Secretary
                      Transaction Systems Architects, Inc.
                             224 South 108th Avenue
                              Omaha, Nebraska 68514
                                 (402) 334-5101
(Name, address and telephone number, including area code, of agent for service)



                         CALCULATION OF REGISTRATION FEE

================================== =================== ===================== ====================== ================
                                                         Proposed Maximum      Proposed Maximum        Amount of
                                      Amount to be      Offering Price Per    Aggregate Offering     Registration
    Title of Securities to be        Registered (1)         Share (2)                Price                Fee
           Registered
================================== =================== ===================== ====================== ================
                                                                                        
1999 STOCK OPTION PLAN              1,000,000 shares         $7.755               $ 7,755,000          $1,938.75
     Class A Common Stock,
     $0.005 par value
- ---------------------------------- ------------------- --------------------- ---------------------- ----------------

1999 EMPLOYEE STOCK                  500,000 shares          $7.755               $ 3,877,500          $ 969.38
   PURCHASE PLAN
     Class A Common Stock,
     $0.005 par value
- ---------------------------------- ------------------- --------------------- ---------------------- ----------------

TOTAL                               1,500,000 shares                              $11,632,500          $2,908.13
================================== =================== ===================== ====================== ================


(1)  Pursuant  to  Rule  416,  this  Registration   Statement  also  covers  any
additional  shares of Class A Common  Stock  which may be  issuable  pursuant to
the antidilution  provisions of the Transaction  Systems  Architects,  Inc. 1999
Stock Option Plan or Transaction  Systems  Architects,  Inc. 1999 Employee Stock
Purchase Plan.

(2)  Estimated   solely  for  purposes  of  calculating  the   registration  fee
pursuant  to Rule 457 (c) and (h).  The price is based  upon the  average of the
high and low  prices of  Transaction  Systems  Architects,  Inc.  Class A Common
Stock on April 23, 2001, as reported on the National  Association  of Securities
Dealers Automated Quotations system.

EXPLANATORY STATEMENT This Registration Statement is filed pursuant to General Instruction E to Form S-8 by Transaction Systems Architects, Inc., a Delaware corporation, in order to register (1) 1,000,000 shares of Class A Common Stock, which shares are in addition to those previously registered on a Registration Statement on Form S-8 (File No. 333-73027) filed with the Securities and Exchange Commission (the "Commission") on February 26, 1999 and on a Registration Statement on Form S-8 (File No. 333-33728) filed with the Commission on March 31, 2000 for issuance pursuant to the Transaction Systems Architects, Inc. 1999 Stock Option Plan, and (2) 500,000 shares of Class A Common Stock, which shares are in addition to those previously registered on the Registration Statement on Form S-8 (File No. 333-73027) filed with the Commission on February 26, 1999. The contents of the Registration Statements on Form S-8 (File Nos. 333-73027 and 333-33728) previously filed with the Commission on February 26, 1999 and March 31, 2000, respectively, are incorporated herein by reference. PART II INFORMATION REQUIRED IN THE REGISTRATION STATEMENT Item 8. Exhibits Exhibit Number ------- 5 Opinion of Baker & McKenzie 23.1 Consent of Arthur Andersen LLP 23.2 Consent of Baker & McKenzie (See Exhibit 5) 24 Power of Attorney (included in Signature Page)

SIGNATURES The Registrant. Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Omaha, State of Nebraska, on this 25th day of April, 2001. TRANSACTION SYSTEMS ARCHITECTS, INC. By:/s/William E. Fisher ------------------------------ William E. Fisher, Chairman, Chief Executive Officer, and Director POWER OF ATTORNEY We, the undersigned officers and directors of Transaction Systems Architects, Inc., hereby severally and individually constitute and appoint William E. Fisher, Dwight G. Hanson and David P. Stokes, and each of them, the true and lawful attorneys and agents of each of us to execute in the name, place and stead of each of us (individually and in any capacity stated below) any and all amendments to this Registration Statement on Form S-8, and all instruments necessary or advisable in connection therewith, and to file the same with the Securities and Exchange Commission, each of said attorneys and agents to have power to act with or without the other and to have full power and authority to do and perform in the name and on behalf of each of the undersigned every act whatsoever necessary or advisable to be done in the premises as fully and to all intents and purposes as any of the undersigned might or could do in person, and we hereby ratify and confirm our signatures as they may be signed by our said attorneys and agents and each of them to any and all such amendments and other instruments. Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the date indicated. Name Title Date - ---- ----- ---- /s/ William E. Fisher Chairman, Chief Executive April 25, 2001 - ---------------------------- Officer and Director William E. Fisher /s/ Dwight G. Hanson Chief Financial Officer April 25, 2001 - ---------------------------- and Senior Vice President Dwight G. Hanson /s/ Edward C. Fuxa Controller April 25, 2001 - --------------------------- Edward C. Fuxa /s/ Charles E. Noell, III Director April 25, 2001 - --------------------------- Charles E. Noell, III /s/ Jim D. Kever Director April 25, 2001 - --------------------------- Jim D. Kever /s/ Larry G. Fendley Director April 25, 2001 - --------------------------- Larry G. Fendley /s/ Roger K. Alexander Director April 25, 2001 - --------------------------- Roger K. Alexander /s/ Gregory J. Duman Director April 25, 2001 - --------------------------- Gregory J. Duman

EXHIBIT INDEX Exhibit Number Description - ------- ------------ 5 Opinion of Baker & McKenzie 23.1 Consent of Arthur Andersen LLP 23.2 Consent of Baker & McKenzie (See Exhibit 5) 24 Power of Attorney (included in Signature Page)



                                                                       Exhibit 5

                                BAKER & McKENZIE
                                Attorneys at Law

                            2300 Trammell Crow Center
                                2001 Ross Avenue
                               Dallas, Texas 75201


                                 April 27, 2001

Board of Directors
Transaction Systems Architects, Inc.
224 South 108th Avenue
Omaha, Nebraska  68154

Re:  Transaction Systems Architects, Inc. (the "Company")

Gentlemen:

         The  Company  has filed with the  Securities  and  Exchange  Commission
(the "Commission") a registration  statement (the  "Registration  Statement") on
Form S-8  under  the  Securities  Act of  1933,  as  amended  (the  "Act").  The
Registration  Statement  covers  (a) 1,000,000  shares of Class A Common  Stock,
par value $.005 per share,  of the Company (the "Stock"),  which shares shall be
issued  pursuant  to the  Company's  1999 Stock  Option  Plan,  as amended  (the
"Option  Plan"),  (b) 500,000  shares of  Stock,  which  shares  shall be issued
pursuant to the Company's  1999 Employee  Stock  Purchase  Plan, as amended (the
"Purchase  Plan,"  together  with the Option Plan,  the  "Plans"),  and (c) such
additional   shares  of  Stock  as  may   become   issuable   pursuant   to  the
anti-dilution  provisions of the Plans (such shares collectively  referred to as
the "Securities").

         We have  acted  as  counsel  to the  Company  in  connection  with  the
preparation  and  filing  of  the  Registration  Statement.  In  rendering  this
opinion we have examined such corporate  records,  documents and  instruments of
the  Company and such  certificates  of public  officials,  have  received  such
representations  from officers of the Company,  and have reviewed such questions
of law as in our judgment are  necessary,  relevant or  appropriate to enable us
to render the opinion  expressed  below.  In such  examination,  we have assumed
the genuineness of all signatures,  the  authenticity of all corporate  records,
documents  and  instruments  submitted to us as  originals,  the  conformity  to
original documents of all documents  submitted to us as conformed,  certified or
photostatic  copies  thereof,  and the  authenticity  of the  originals  of such
conformed, certified or photostatic copies.

         Based upon such  examination and review and upon  representations  made
to us by officers of the Company,  we are of the opinion that upon  issuance and
delivery  of  the  Securities  in  accordance  with  the  applicable  terms  and
conditions   of  the  Plans  and  upon  receipt  by  the  Company  of  the  full
consideration  for the  Securities  as  determined  pursuant  to the Plans,  the
Securities will be legally issued, fully paid and nonassessable.

         This firm  consents to the filing of this  opinion as an exhibit to the
Registration  Statement.  In giving such  consent,  we do not admit that we come
within the  category  of persons  whose  consent is required by Section 7 of the
Act or the rules and regulations of the Commission thereunder.



                                              Very truly yours,




                                              /s/Baker & McKenzie


                                                                    Exhibit 23.1



Consent of independent public accountants


As independent  public  accountants,  we hereby consent to the  incorporation by
reference  in this  Registration  Statement  on  Form  S-8 of our  report  dated
October 26, 2000,  included in  Transaction  Systems  Architects,  Inc.'s Annual
Report on Form 10-K for the fiscal year ended  September  30,  2000,  and to all
references to our Firm included in this Registration Statement.


Arthur Andersen LLP

Omaha, Nebraska,
April 25, 2001