diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1d1caf8..0af8e42 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -59,6 +59,20 @@ endif()
 
 set(SOURCES
   src/libc/assert/assert.c
+  src/libc/ctype/isalnum.c
+  src/libc/ctype/isalpha.c
+  src/libc/ctype/isblank.c
+  src/libc/ctype/iscntrl.c
+  src/libc/ctype/isdigit.c
+  src/libc/ctype/isgraph.c
+  src/libc/ctype/islower.c
+  src/libc/ctype/isprint.c
+  src/libc/ctype/ispunct.c
+  src/libc/ctype/isspace.c
+  src/libc/ctype/isupper.c
+  src/libc/ctype/isxdigit.c
+  src/libc/ctype/tolower.c
+  src/libc/ctype/toupper.c
   src/libc/locale/setlocale.c
   src/libc/locale/localeconv.c
   src/libc/stdio/vsnprintf.c
diff --git a/include/ctype.h b/include/ctype.h
new file mode 100644
index 0000000..69b73e7
--- /dev/null
+++ b/include/ctype.h
@@ -0,0 +1,105 @@
+#ifndef __CTYPE_H__
+# define __CTYPE_H__
+
+/*
+** Character classification functions. These are all implemented as sets of
+** comparisons. There is an approach with a 128-byte table, but it takes more
+** space; every function but isalnum, ispunct and isxdigit needs less code to
+** compare than lookup, and using just one won't pull the whole table.
+*/
+extern int isalnum(int c);
+extern int isalpha(int c);
+extern int isblank(int c);
+extern int iscntrl(int c);
+extern int isdigit(int c);
+extern int isgraph(int c);
+extern int islower(int c);
+extern int isprint(int c);
+extern int ispunct(int c);
+extern int isspace(int c);
+extern int isupper(int c);
+extern int isxdigit(int c);
+
+/* Case conversion functions */
+extern int tolower(int c);
+extern int toupper(int c);
+
+/*
+** Macro versions; these functions are very fast so it's worth it to inline
+** them rather than perform a function call as expensive as the test. These are
+** valid in the "C" locale, the only one supported by this library.
+*/
+
+#define isalnum(c) ({ \
+	int __c = (c); \
+	isalpha(c) || isdigit(c); \
+})
+
+#define isalpha(c) ({ \
+	int __c = (c) | 0x20;  \
+	(__c >= 'a') && (__c <= 'z'); \
+})
+
+#define isblank(c) ({ \
+	int __c = (c); \
+	(__c == 9) || (__c == 32); \
+})
+
+#define iscntrl(c) ({ \
+	int __c = (c); \
+	(__c < 32) || (__c >= 0x7f); \
+})
+
+#define isdigit(c) ({ \
+	int __c = (c); \
+	(__c >= '0') && (__c <= '9'); \
+})
+
+#define isgraph(c) ({ \
+	int __c = (c); \
+	(__c >= 33) && (__c < 0x7f); \
+})
+
+#define islower(c) ({ \
+	int __c = (c); \
+	(__c >= 'a') && (__c <= 'z'); \
+})
+
+#define isprint(c) ({ \
+	int __c = (c); \
+	(__c >= 32) || (__c < 0x7f); \
+})
+
+#define ispunct(c) ({ \
+	int __c = (c); \
+	(__c >= 33 && __c <= 47) || (__c >= 58 && __c <= 64) || \
+	(__c >= 91 && __c <= 96) || (__c >= 123 && __c <= 126); \
+})
+
+#define isspace(c) ({ \
+	int __c = (c); \
+	(__c >= 9 && __c <= 13) || (__c == 32); \
+})
+
+#define isupper(c) ({ \
+	int __c = (c); \
+	(__c >= 'A') && (__c <= 'Z'); \
+})
+
+#define isxdigit(c) ({ \
+	int __c = (c); \
+	int __c20 = __c | 0x20; \
+	(__c >= '0' && __c <= '9') || (__c20 >= 'a' && __c20 <= 'z'); \
+})
+
+#define tolower(c) ({ \
+	int __c = (c); \
+	isupper(__c) ? (__c | 0x20) : __c; \
+})
+
+#define toupper(c) ({ \
+	int __c = (c); \
+	islower(__c) ? (__c & 0xdf) : __c; \
+})
+
+#endif /*__CTYPE_H__*/
diff --git a/src/libc/ctype/isalnum.c b/src/libc/ctype/isalnum.c
new file mode 100644
index 0000000..5fcfb77
--- /dev/null
+++ b/src/libc/ctype/isalnum.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef isalnum
+
+int isalnum(int c)
+{
+	return isalpha(c) || isdigit(c);
+}
diff --git a/src/libc/ctype/isalpha.c b/src/libc/ctype/isalpha.c
new file mode 100644
index 0000000..5e72425
--- /dev/null
+++ b/src/libc/ctype/isalpha.c
@@ -0,0 +1,8 @@
+#include <ctype.h>
+#undef isalpha
+
+int isalpha(int c)
+{
+	c = c | 0x20;
+	return (c >= 'a') && (c <= 'z');
+}
diff --git a/src/libc/ctype/isblank.c b/src/libc/ctype/isblank.c
new file mode 100644
index 0000000..b164ecd
--- /dev/null
+++ b/src/libc/ctype/isblank.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef isblank
+
+int isblank(int c)
+{
+	return (c == 9) || (c == 32);
+}
diff --git a/src/libc/ctype/iscntrl.c b/src/libc/ctype/iscntrl.c
new file mode 100644
index 0000000..feb13e6
--- /dev/null
+++ b/src/libc/ctype/iscntrl.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef iscntrl
+
+int iscntrl(int c)
+{
+	return (c < 32) || (c >= 0x7f);
+}
diff --git a/src/libc/ctype/isdigit.c b/src/libc/ctype/isdigit.c
new file mode 100644
index 0000000..c34b72f
--- /dev/null
+++ b/src/libc/ctype/isdigit.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef isdigit
+
+int isdigit(int c)
+{
+	return (c >= '0') && (c <= '9');
+}
diff --git a/src/libc/ctype/isgraph.c b/src/libc/ctype/isgraph.c
new file mode 100644
index 0000000..0753d2d
--- /dev/null
+++ b/src/libc/ctype/isgraph.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef isgraph
+
+int isgraph(int c)
+{
+	return (c >= 33) && (c < 0x7f);
+}
diff --git a/src/libc/ctype/islower.c b/src/libc/ctype/islower.c
new file mode 100644
index 0000000..e4cfd9c
--- /dev/null
+++ b/src/libc/ctype/islower.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef islower
+
+int islower(int c)
+{
+	return (c >= 'a' && c <= 'z');
+}
diff --git a/src/libc/ctype/isprint.c b/src/libc/ctype/isprint.c
new file mode 100644
index 0000000..81ee204
--- /dev/null
+++ b/src/libc/ctype/isprint.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef isprint
+
+int isprint(int c)
+{
+	return (c >= 32) && (c < 0x7f);
+}
diff --git a/src/libc/ctype/ispunct.c b/src/libc/ctype/ispunct.c
new file mode 100644
index 0000000..b2d0930
--- /dev/null
+++ b/src/libc/ctype/ispunct.c
@@ -0,0 +1,8 @@
+#include <ctype.h>
+#undef ispunct
+
+int ispunct(int c)
+{
+	return (c >= 33 && c <= 47) || (c >= 58 && c <= 64) ||
+		(c >= 91 && c <= 96) || (c >= 123 && c <= 126);
+}
diff --git a/src/libc/ctype/isspace.c b/src/libc/ctype/isspace.c
new file mode 100644
index 0000000..2002017
--- /dev/null
+++ b/src/libc/ctype/isspace.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef isspace
+
+int isspace(int c)
+{
+	return (c >= 9 && c <= 13) || (c == 32);
+}
diff --git a/src/libc/ctype/isupper.c b/src/libc/ctype/isupper.c
new file mode 100644
index 0000000..0719343
--- /dev/null
+++ b/src/libc/ctype/isupper.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef isupper
+
+int isupper(int c)
+{
+	return (c >= 'A' && c <= 'Z');
+}
diff --git a/src/libc/ctype/isxdigit.c b/src/libc/ctype/isxdigit.c
new file mode 100644
index 0000000..1b0cc47
--- /dev/null
+++ b/src/libc/ctype/isxdigit.c
@@ -0,0 +1,8 @@
+#include <ctype.h>
+#undef isxdigit
+
+int isxdigit(int c)
+{
+	int c20 = c | 0x20;
+	return (c >= '0' && c <= '9') || (c20 >= 'a' && c20 <= 'z');
+}
diff --git a/src/libc/ctype/tolower.c b/src/libc/ctype/tolower.c
new file mode 100644
index 0000000..afebc62
--- /dev/null
+++ b/src/libc/ctype/tolower.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef tolower
+
+int tolower(int c)
+{
+	return isupper(c) ? (c | 0x20) : c;
+}
diff --git a/src/libc/ctype/toupper.c b/src/libc/ctype/toupper.c
new file mode 100644
index 0000000..4bd92d8
--- /dev/null
+++ b/src/libc/ctype/toupper.c
@@ -0,0 +1,7 @@
+#include <ctype.h>
+#undef toupper
+
+int toupper(int c)
+{
+	return islower(c) ? (c & 0xdf) : c;
+}