FORM 6-K                                    
                                                                                
                       SECURITIES AND EXCHANGE COMMISSION                       
                             Washington, D.C. 20549                             
                                                                                
                            Report of Foreign Issuer                            
                                                                                
                      Pursuant to Rule 13a-16 or 15d-16 of                      
                      the Securities Exchange Act of 1934                       
                                                                                
                           For the month ofMay, 2024                            
                                                                                
                        Commission FileNumber: 001-12518                        
                                                                                
                             Banco Santander, S.A.                              
             (Exact name ofregistrant as specified in its charter)              
                                                                                
                             Ciudad Grupo Santander                             
                    28660 Boadilla del Monte (Madrid) Spain                     
                     (Address of principalexecutive office)                     
                                                                                
                                                                                
Indicate by check mark whether the registrantfiles or will file annual reports 
under cover of Form 20-F or Form 40-F:


Form 20-F X  Form 40-F 







                                                                                

                              Banco Santander,S.A.                              
                                                                                
                               TABLE OF CONTENTS                                
                                                                                

Item                                                        
                                                            
 1   Report of Other Relevant Information dated May 23, 2024

                                                                                

                                                                           Item1
                                                                                



Banco Santander, S.A.
(the "
Bank
"or "
Banco Santander
"), in compliance with the Securities Market legislation, hereby communicates 
the following:

                           OTHER RELEVANT INFORMATION                           
                                                                                
Reference is madeto our notice of inside information of 19 February 2024 
(official registry number 2114)
(the "
Buy-back Commencement Communication
"),relating to the buyback programme of own shares (the "
Buy-back Programme
") approved by the Board of Directors of BancoSantander.

Pursuant to article 5 of Regulation (EU) no. 596/2014on Market Abuse of 16 
April 2014, and articles 2.2 and 2.3 of Commission Delegated Regulation (EU) 
2016/1052, of 8 March 2016, the Bankinforms of the transactions carried out 
over its own shares between 17 and 22 May 2024 (both inclusive).

The cash amount of the shares purchased to 22 May2024 as a result of the 
execution of the Buy-back Programme amounts to 1,077,666,184 Euros, which 
represents approximately 73.9% of themaximum investment amount of the Buy-back 
Programme. The programme was announced together with its other characteristics 
through the Buy-backCommencement Communication.


   Date    Security Transaction Trading venue Number of shares Weighted average price (€)
17/05/2024   SAN     Purchase       XMAD         2,099,941                 4.8310             
17/05/2024   SAN     Purchase       CEUX          625,171                  4.8320             
17/05/2024   SAN     Purchase       TQEX           93,525                  4.8297             
17/05/2024   SAN     Purchase       AQEU          181,363                  4.8331             
20/05/2024   SAN     Purchase       XMAD         2,378,516                 4.8741             
20/05/2024   SAN     Purchase       CEUX          485,518                  4.8737             
20/05/2024   SAN     Purchase       TQEX           79,978                  4.8733             
20/05/2024   SAN     Purchase       AQEU          155,988                  4.8735             
21/05/2024   SAN     Purchase       XMAD         2,098,908                 4.8268             
21/05/2024   SAN     Purchase       CEUX          612,050                  4.8261             
21/05/2024   SAN     Purchase       TQEX           84,014                  4.8313             
21/05/2024   SAN     Purchase       AQEU          205,028                  4.8268             
22/05/2024   SAN     Purchase       XMAD         2,578,701                 4.8301             
22/05/2024   SAN     Purchase       CEUX          616,780                  4.8351             
22/05/2024   SAN     Purchase       TQEX           88,982                  4.8400             
22/05/2024   SAN     Purchase       AQEU          215,537                  4.8333             
                                    TOTAL        12,600,000                                   


Issuer name
: Banco Santander, S.A. - LEI5493006QMFDDMYWIAM13

Reference of the financial instrument
: ordinaryshares - Code ISIN ES0113900J37

Detailed information of the transactions carriedout within the referred period 
is attached as Annex I.

                                        Boadilla del Monte (Madrid), 23 May 2024
                                                                                
                                                                               1

                                    ANNEX I                                     
                                                                                
Detailedinformation on each of the transactions carried out within the context 
of the Buy-back Programme between 17/05/2024 and 22/05/2024 (bothinclusive)

(https://www.santander.com/content/dam/santander-com/es/documentos/cumplimiento/
do-anexo-i-17-may-a-22-may.pdf)

                                                                                
                                                                               2

                                   SIGNATURE                                    
                                                                                
Pursuant to therequirements of the Securities Exchange Act of 1934, the 
registrant has duly caused this report to be signed on its behalf by the 
undersigned,thereunto duly authorized.


                   Banco Santander, S.A.                   
                                                           
                                                           
Date: May 23, 2024 By: /s/ Pedro de Mingo Kaminouchi       
                       Name:  Pedro de Mingo Kaminouchi    
                       Title: Head of Regulatory Compliance


                                                                                
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