March 1, 2019

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

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

Dear Mr. Butterfield:

       We have reviewed your 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.

Draft Registration Statement on Form S-1

Our Business Model, page 4

1.     Provide your definition of Net Dollar Retention Rate where you first
mention it in the
       prospectus.
2.     To provide context, disclose whether the 9 million daily active users
you reference
       include users of your free version. Please clarify if the statement that
your users are
       highly engaged also describes the activity of your customers that use
your free version.
 Stewart Butterfield
FirstName LastNameStewart Butterfield
Slack Technologies, Inc.
Comapany NameSlack Technologies, Inc.
March 1, 2019
March 1, 2019 Page 2
Page 2
FirstName LastName
Our Market Opportunity, page 5

3.       With respect to your estimate of the size of the market opportunity
for Slack here and on
         page 92, clarify your disclosure by addressing the scope of your
estimate. For example,
         disclose whether management views this as the size of the market
opportunity for other
         workplace communication companies as a whole, or if it is specific to
Slack. Also,
         balance this disclosure with a discussion of the increasing number of
competitors in the
         industry and clarify that your estimate may not be reflective of the
actual market for your
         product.
Risk Factors
A security incident may allow unauthorized access to our systems, networks, or
data or our
customers' data, harm our reputation..., page 19

4.       Summarize the material details of your March 2015 security incident.
5.       Describe the nature of the board's role in overseeing cybersecurity
risk management.
Risks Related to Ownership of Our Class A Common Stock, page 44

6.       We note that your restated certificate of incorporation contains a
corporate opportunity
         waiver provision. Discuss the scope of this provision, and explain how
it will impact
         holders of your common stock. For example, describe how any potential
conflict of
         interest could have a material adverse effect on your business,
financial condition, results
         of operations, or prospects.
The public price of our Class A common stock may be volatile, and could, upon
listing...decline
significantly and rapidly, page 45

7.       You disclose that your financial advisors "will be available to
consult with the designated
         market marker," who will be setting the opening public price of your
Class A common
         stock. Clarify that the applicable listing rules require consultation
between the DMM and
         the financial advisor(s) regarding the ownership of the Company's
common stock and pre-
         listing selling and buying interest in the Company's common stock that
the financial
         advisors become aware of from potential investors and holders of
common stock (e.g.,
         holders of RSUs).
8.       Discuss whether brand awareness or recognition of your product by
retail investors might
         factor into demand for your shares upon listing. Address whether any
perceived or actual
         lack of consumer awareness of the Company may increase volatility in
the share price.
 Stewart Butterfield
FirstName LastNameStewart Butterfield
Slack Technologies, Inc.
Comapany NameSlack Technologies, Inc.
March 1, 2019
March 1, 2019 Page 3
Page 3
FirstName LastName
The dual class structure of our common stock has the effect of concentrating
voting control...,
page 48

9.       Disclose the risk that due to the Company's dual class share
structure, the Company's
         Class A common stock may be ineligible for inclusion in certain stock
market indices,
         which could adversely affect share price and liquidity.
10.      Disclose that any future issuances of Class B shares may be dilutive
to Class A
         stockholders. Also address any risks associated with the possibility
that one or more
         institutions currently holding your Class B stock may gain outsized
voting control if other
         Class B holders sell or otherwise convert their shares. We note that
four of your current
         Class B stockholders currently hold, together, over 54% of voting
shares.
Our amended and restated bylaws will designate a state or federal court located
within the State
of Delaware as the exclusive forum..., page 51

11.      We note your risk factor disclosure that your amended and restated
bylaws identify the
         Court of Chancery of the State of Delaware (subject to certain
exceptions) as the exclusive
         forum for certain litigation, including any "derivative action." We
also note your
         disclosure on page 133 that the federal district court for the
District of Delaware will have
         alternate jurisdiction for such claims. Please disclose whether this
provision applies solely
         to state law claims. If it does not apply solely to state law claims,
then please note that
         that Section 27 of the Exchange Act creates exclusive federal
jurisdiction over all suits
         brought to enforce any duty or liability created by the Exchange Act
or the rules and
         regulations thereunder and Section 22 of the Securities Act creates
concurrent jurisdiction
         for federal and state courts over all suits brought to enforce any
duty or liability created by
         the Securities Act or the rules and regulations thereunder. If this
provision is intended to
         apply solely to state law claims, please also ensure that the
exclusive forum provision in
         the amended and restated bylaws states this clearly.
RSU Sales, page 55

12.      Explain why the listing of your Class A shares will result in the
vesting and settlement of
         outstanding RSUs. Disclose the possibility that such sales could
result in an overhang of
         shares available, which could in turn affect the share price and
orderly trading.
13.      Clarify whether RSUs that vest and settle on the first day of trading
expose their holders
         to out-of-pocket tax liability if opening trading is volatile
resulting in the supply of shares
         far exceeding the demand for the Company's shares.
 Stewart Butterfield
FirstName LastNameStewart Butterfield
Slack Technologies, Inc.
Comapany NameSlack Technologies, Inc.
March 1, 2019
March 1, 2019 Page 4
Page 4
FirstName LastName
Capitalization, page 57

14.      Your disclosures on page F-8 suggest that the unaudited pro forma
balance sheet
         information in your financial statements will give effect to RSUs that
are expected to vest
         and settle upon listing of the Class A common stock. Please tell us
why the pro forma
         column of your capitalization table on page 57 excludes the impact of
vesting RSUs.
Selected Consolidated Financial Data and Other Data, page 59

15.      Please revise your consolidated balance sheet data table on page 60 to
include a pro forma
         column similar to the one provided on page 10.
Key Business Metrics, page 60

16.      We note that you consider your ability to convert customers who use
your free
         subscription plan into paying customers an important part of your
business model (page
         64). Therefore, you should provide metrics on the number of non-paying
customers and
         number of non-paying customers converted to paid customers for the
periods being
         presented.
Management's Discussion and Analysis of Financial Condition and Results of
Operations
Overview, page 62

17.      Discuss management's plan for profitability in light of your net
losses for the years ended
         January 31, 2017 and 2018.
Factors Affecting our Performance, page 64

18.      Explain the importance of monthly recurring revenue and annual
recurring revenue to
         evaluating the financial condition and operations of your business.
Clarify how ARR
         differs from MRR, whether MRR takes into account revenue from
customers across all of
         your subscription plans, and whether MRR is calculated on an annual or
quarterly basis.
Our Subscription Plans, page 97

19.      Provide a breakdown in the number of your Free, Standard, Plus and
Enterprise Grid
         customers.
Competition, page 103

20.      Include a brief discussion of competitors that may offer a niche
service or more narrow
         product offering. Explain how management views any such competitors
offering a free or
         discounted service.
 Stewart Butterfield
FirstName LastNameStewart Butterfield
Slack Technologies, Inc.
Comapany NameSlack Technologies, Inc.
March 1, 2019
March 1, 2019 Page 5
Page 5
FirstName LastName
Executive Compensation
Summary Compensation Table, page 112

21.      We note that your summary compensation table is blank and includes
placeholders only
         for 2019. In your next amendment, revise your executive and director
compensation
         section to include all required disclosures.
Executive Employment Arrangements, page 113

22.      Disclose the material terms of the confirmatory offer letters that you
plan to enter into
         with each of your named executive officers and the purpose of such
agreements.
Principal and Registered Stockholders, page 126

23.      We note your statement that you "will have no input if and when any
Registered
         Stockholder may, or may not, elect to sell their shares of common
stock or the prices at
         which any such sales may occur." Qualify this statement with
disclosure about how the
         Company will facilitate immediate sales of common stock on behalf of
the Registered
         Stockholders who hold vesting RSUs.
24.      Include a separate line entry in the table reflecting the group of
Registered Stockholders
         holding RSUs who are expected to sell their common stock immediately.
Description of Capital Stock
Class A Common Stock and Class B Common Stock
Conversion, page 131

25.      Describe each of the "certain permitted transfers" that will not
result in Class B common
         stock automatically converting into Class A common stock.
26.      Discuss the purpose of the "sunset provision" for your Class B common
stock, and the
         effect this provision may have on the concentration of voting power of
your stock in the
         future.
Sale Price History of Our Common Stock, page 138

27.      Clarify whether there have been any private transactions in your Class
A common stock,
         and if so, disclose the high and low sales prices of those private
transactions for the
         relevant periods. Also clarify whether the DMM in consultation with
your financial
         advisors is expected under applicable NYSE Listing Rules to consider
the private trading
         history of the Class B common stock in setting the opening public
price.
 Stewart Butterfield
Slack Technologies, Inc.
March 1, 2019
Page 6
Plan of Distribution, page 143

28.      You state that your financial advisors are expected to provide input
to the DMM regarding
         their understanding of the ownership of your outstanding common stock
and pre-listing
         selling and buying interest in your Class A common stock. Disclose
how, in accordance
         with this process, Morgan Stanley and your other financial advisors
will become aware of
         pre-listing selling and buying interest in your Class A common stock.
For example, state
         whether the advisors will consult with Registered Stockholders,
including institutional
         investors and RSU holders.
29.      We note that there has been private trading in your Class B common
stock during the last
         twelve months. Clarify whether the DMM in consultation with your
financial advisors
         will consider these trades in determining the opening public price.
Consolidated Financial Statements
Note 1. Description of Business and Summary of Significant Accounting Policies
Revenue Recognition, page F-9

30.      Please provide us with a specific and comprehensive discussion of the
terms in certain of
         your contracts that give you the right to bill for additional usage.
Clarify why this usage is
         not included in your transaction price. Reference ASC 606-10-32-5.
General

31.      We note your dependence on services from Amazon Web Services to
maintain your
         infrastructure. Accordingly, please file your amended agreement with
AWS as an exhibit
         to the registration statement. Refer to Item 601(b)(10)(ii)(B) of
Regulation S-K.
32.      Supplementally provide us with copies of your agreements with your
financial advisors.
        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 1, 2019 Page 6                                            Office of
Telecommunications
FirstName LastName