March 21, 2019

Stewart Butterfield
Chief Executive Officer
Slack Technologies, Inc.
500 Howard Street
San Francisco, CA 94105

       Re: Slack Technologies, Inc.
           Amendment No. 1 to
           Draft Registration Statement on Form S-1
           Submitted March 12, 2019
           CIK No. 0001764925

Dear Mr. Butterfield:

      We have reviewed your amended draft registration statement and have the
following
comments. In some of our comments, we may ask you to provide us with
information so we
may better understand your disclosure.

       Please respond to this letter by providing the requested information and
either submitting
an amended draft registration statement or publicly filing your registration
statement on
EDGAR. If you do not believe our comments apply to your facts and circumstances
or do not
believe an amendment is appropriate, please tell us why in your response.

      After reviewing the information you provide in response to these comments
and your
amended draft registration statement or filed registration statement, we may
have additional
comments.

Amendment No. 1 to Draft Registration Statement on Form S-1

Risk Factors
Risks Related to Our Business, page 13

1.     Highlight in your risk factor disclosure that your customers can and do
subscribe to
       multiple subscription plans simultaneously and explain why they might
choose to do so.
       Discuss any associated risks, such as the possibility that your
customers may only upgrade
       to a higher tier subscription temporarily and that varying subscriptions
tiers among single
       customers may make it more difficult for you to track your financial
performance and key
       performance metrics.
 Stewart Butterfield
FirstName LastNameStewart Butterfield
Slack Technologies, Inc.
Comapany2019
March 21, NameSlack Technologies, Inc.
March 21, 2019 Page 2
Page 2
FirstName LastName
RSU Sales, page 57

2.       We note that the number of shares to be sold for the purpose of
funding personal tax
         withholding obligations is blank. We also note that the number of
shares an employee
         will have to sell is dependent upon a number of factors, including the
share price at the
         time of settlement. Please advise as to how the number of shares will
be known prior to
         effectiveness given that the opening trading price will not be known
to the Company nor
         its financial advisors until after effectiveness.
Capitalization, page 59

3.       We note your response to our prior comment 14. Your revised
disclosures on page 59
         indicate that the pro forma column of your capitalization table will
give effect to the
         vesting and settlement of RSUs for which you expect the performance
vesting condition to
         be satisfied upon the listing of your Class A common stock. However,
in the second
         bullet point on page 60, you also indicate that the pro forma column
of your capitalization
         table excludes certain RSUs that will settle and vest upon the listing
of your Class A
         common stock. Please revise to address this apparent inconsistency.
Selected Consolidated Financial Data and Other Data, page 61

4.       We note your response to our prior comment 15. Although Item 301 of
Regulation of S-K
         does not specifically require pro forma balance sheet data be
disclosed, factors that may
         materially affect the comparability of the selected financial data
should be discussed.
         Please refer to Instructions 1 and 2 to Item 301 of Regulation S-K and
consider adding a
         pro forma column to your consolidated balance sheet data table on page
62.
Management's Discussion and Analysis of Financial Condition and Results of
Operations
Key Business Metrics, page 68

5.       You indicate that the Net Dollar Retention Rate metric helps measure
the rate of
         expansion within your paid customer base. We note that your Net Dollar
Retention Rate
         has declined from 171% as of January 31, 2017 to 143% as of January
31, 2019. Please
         provide an analysis of this metric, including a discussion of what the
decline in the metric
         indicates about your prospects for revenue growth and profitability.
6.       You disclose that your revenue growth and profitability depend, in
part, on your ability to
         convert organizations on your free version to paid customers. In that
respect, we note
         your response to comment 16 and believe that the number of
organizations on your free
         version that converted to paid customers for the relevant periods
should be disclosed.
         Alternatively, disclose how management tracks conversion of
organizations on your free
         version to paid customers, whether as an absolute number or a
percentage of revenue
         increases.
 Stewart Butterfield
Slack Technologies, Inc.
March 21, 2019
Page 3
Our Subscription Plans, page 99

7.       We note your response to comment 19 and your assertion that adding up
the number of
         customers on each of the Standard, Plus and Enterprise Grid
subscription plans will
         overstate the Company's number of Paid Customers. Instead, please
provide narrative
         disclosure indicating the relative percentages of your subscribers
that upgrade from your
         standard paid subscription to your plus and/or enterprise grid
subscriptions. You should
         also provide disclosure of any metrics or measures that management
uses to track your
         paid customers' upgrading activities and/or the total percent of your
revenues derived from
         each of your subscription plan options.
Executive Compensation
2019 Summary Compensation Table, page 114

8.       Provide executive compensation disclosure in your summary compensation
table for each
         of the last two completed fiscal years. See Instruction 1 to Item
402(c) of Regulation S-K.
Principal and Registered Stockholders, page 130

9.       Confirm that the registered stockholders table on page 132 reflects
all of the outstanding
         holders of your common stock.
10.      We note your response to prior comment 24, yet it is not clear whether
the table entry
         entitled "Holders of RSUs" includes all the Class A shares that are
expected to be sold in
         Sell-to-Cover Transactions. In this regard, footnotes 19 and 20 to the
entries "All Other
         Employees" and "All Other Registered Stockholders" include RSUs for
which the service
         condition has been or will be satified within 60 days of January 31,
2019. Therefore, it
         appears that these entries also include Class A shares that are
expected to be sold in Sell-
         to-Cover Transactions. Please advise.
        You may contact Lisa Etheredge, Staff Accountant, at (202) 551-3424 or
Robert S.
Littlepage, Accounting Branch Chief, at (202) 551-3361 if you have questions
regarding
comments on the financial statements and related matters. Please contact Joshua
Shainess,
Attorney-Adviser, at (202) 551-7951 or Larry Spirgel, Assistant Director, at
(202) 551-3810 with
any other questions.



FirstName LastNameStewart Butterfield                          Sincerely,
Comapany NameSlack Technologies, Inc.
                                                               Division of
Corporation Finance
March 21, 2019 Page 3                                          Office of
Telecommunications
FirstName LastName