diff --git a/src/core/Buffer.cc b/src/core/Buffer.cc
index 9be4742..82d7d53 100644
--- a/src/core/Buffer.cc
+++ b/src/core/Buffer.cc
@@ -146,3 +146,18 @@ bool Buffer::write_to_file(const char * filename)
 
     return true;
 }
+
+void Buffer::enter_insert_mode(const Buffer::Iterator & position)
+{
+    m_insert_position = position.offset();
+    if (m_insert_position > m_gap_buffer->size())
+    {
+        m_insert_position = 0;
+    }
+    m_insert_mode = true;
+}
+
+void Buffer::exit_insert_mode()
+{
+    m_insert_mode = false;
+}
diff --git a/src/core/Buffer.h b/src/core/Buffer.h
index ab5cbee..d4e4f7b 100644
--- a/src/core/Buffer.h
+++ b/src/core/Buffer.h
@@ -78,6 +78,7 @@ public:
             return m_offset >= other.m_offset;
         }
         size_t line() const { return m_line; }
+        size_t offset() const { return m_offset; }
 
     protected:
         Buffer * m_buffer;
@@ -99,6 +100,9 @@ public:
     uint8_t * address(size_t offset) const { return m_gap_buffer->address(offset); }
     Encoding::Type encoding() const { return m_encoding; }
     uint8_t tabstop() const { return m_tabstop; }
+    void enter_insert_mode(const Buffer::Iterator & position);
+    void exit_insert_mode();
+    bool insert_mode() const { return m_insert_mode; }
 
 protected:
     bool m_eol_at_eof;
@@ -106,6 +110,8 @@ protected:
     std::shared_ptr<GapBuffer> m_gap_buffer;
     Encoding::Type m_encoding;
     uint8_t m_tabstop;
+    bool m_insert_mode;
+    size_t m_insert_position;
 
     void common_initialization();
     bool load_from_file(const char * filename);