diff --git a/Doc/library/os.rst b/Doc/library/os.rst
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -1103,10 +1103,14 @@
 
 .. function:: readv(fd, buffers)
 
-   Read from a file descriptor into a number of writable buffers. *buffers* is
-   an arbitrary sequence of writable buffers. Returns the total number of bytes
-   read.
-
+   Read from a file descriptor *fd* into a number of mutable
+   :term:`bytes-like objects <bytes-like object>`
+   ("buffers"). :func:`~os.readv` will transfer data into each buffer
+   until it is full and then move on to the next buffer in the
+   sequence to hold the rest of the data. :func:`~os.readv` returns
+   the total number of bytes read (which may be less than the total
+   capacity of all the objects).
+          
    Availability: Unix.
 
    .. versionadded:: 3.3
@@ -1155,10 +1159,11 @@
 
 .. function:: writev(fd, buffers)
 
-   Write the contents of *buffers* to file descriptor *fd*, where *buffers*
-   is an arbitrary sequence of buffers.
-   Returns the total number of bytes written.
-
+   Write the contents of *buffers* to file descriptor *fd*. *buffers*
+   must be a sequence of :term:`bytes-like objects <bytes-like
+   object>`.  :func:`~os.writev` writes the contents of each object to the file
+   descriptor and returns the total number of bytes written.
+   
    Availability: Unix.
 
    .. versionadded:: 3.3
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -84,6 +84,9 @@
 
 - Issue #14455: Fix some problems with the new binary plist support in plistlib.
 
+- Issue #17811: Improve documentation of os.writev and os.readv. Patch
+  by Nikolaus Rath.
+
 IDLE
 ----
 
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -8061,9 +8061,12 @@
 #ifdef HAVE_READV
 PyDoc_STRVAR(posix_readv__doc__,
 "readv(fd, buffers) -> bytesread\n\n\
-Read from a file descriptor into a number of writable buffers. buffers\n\
-is an arbitrary sequence of writable buffers.\n\
-Returns the total number of bytes read.");
+Read from a file descriptor fd into a number of mutable, bytes-like\n\
+objects (\"buffers\").  readv will transfer data into each buffer\n\
+until it is full and then move on to the next buffer in the sequence\n\
+to hold the rest of the data.\n\n\
+readv returns the total number of bytes read (which may be less than\n\
+the total capacity of all the buffers.");
 
 static PyObject *
 posix_readv(PyObject *self, PyObject *args)
@@ -8457,9 +8460,10 @@
 #ifdef HAVE_WRITEV
 PyDoc_STRVAR(posix_writev__doc__,
 "writev(fd, buffers) -> byteswritten\n\n\
-Write the contents of buffers to a file descriptor, where buffers is an\n\
-arbitrary sequence of buffers.\n\
-Returns the total bytes written.");
+Write the contents of *buffers* to file descriptor *fd*. *buffers*\n\
+must be a sequence of bytes-like objects.\n\n\
+writev writes the contents of each object to the file descriptor\n\
+and returns the total number of bytes written.");
 
 static PyObject *
 posix_writev(PyObject *self, PyObject *args)